Hemangio-colony forming cells

ABSTRACT

Methods of generating and expanding human hemangio-colony forming cells in vitro and methods of expanding and using such cells are disclosed. The methods permit the production of large numbers of hemangio-colony forming cells as well as derivative cells, such as hematopoietic and endothelial cells. The cells obtained by the methods disclosed may be used for a variety of research, clinical, and therapeutic applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §120 asa continuation of U.S. patent application Ser. No. 13/190,988, filedJul. 26, 2011, allowed Jun. 29, 2015, which is a continuation of U.S.patent application Ser. No. 11/787,262, filed Apr. 13, 2007, now U.S.Pat. No. 8,017,393 issued Sep. 13, 2011, which claims the benefit ofpriority under 35 U.S.C. §119 of U.S. Provisional Application No.60/792,224, filed Apr. 14, 2006, U.S. Provisional Application No.60/801,993, filed May 19, 2006, U.S. Provisional Application No.60/846,163, filed Sep. 20, 2006, U.S. Provisional Application No.60/852,142, filed Oct. 16, 2006, U.S. Provisional Application No.60/860,676, filed Nov. 22, 2006, and U.S. Provisional Application No.60/918,832, filed Mar. 19, 2007, the entirety of which is herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention generally relates to methods for generating andexpanding human hemangio-colony forming cells. More particularly, theinvention relates to a method of generating and expanding humanhemangio-colony forming cells in vitro using a two-step process byfirst, culturing human embryo-derived stem cells in serum-free media inthe presence of at least one growth factor in an amount sufficient toinduce the differentiation of embryonic stem cells into embryoid bodies,and second, culturing the embyroid bodies in serum-free media in thepresence of at least one growth factor in an amount sufficient to expandhuman hemangio-colony forming cells in the medium comprising embryoidbodies. The invention further relates to preparations of humanhemangio-colony forming cells. The invention further relates to methodsof differentiating human hemangio-colony forming units along ahematopoietic or endothelial lineage, as well as methods of preparingpartially or fully differentiated cell types from hemangio-colonyforming cells. Hemangio-colony forming cells, and cells differentiatedtherefrom, have a variety of uses in vitro and in vivo. The ability togenerate expanded human hemangio-colony forming cells in such largequantities in vitro provides for the first time the potential to derivelarge numbers of human hemangio-colony forming derivative cell types,such as human hematopoietic stem cells, or endothelial cells,differentiated hematopoietic cells, such as red blood cells andplatelets, that will be useful in various therapeutic applications.Furthermore, the expanded numbers of human hemangio-colony forming cellsderived by the present invention may be utilized in novel therapeuticstrategies in the treatment of hematopoietic and endothelial celldisorders or in blood banking.

BACKGROUND OF THE INVENTION

Hematopoietic stem cells (HSCs) are capable of self-renewal and are ableto give rise to all blood cell lineages. These cells, which reside inthe bone marrow, form the basis of the adult hematopoietic system. Thetransplantation of these cells represents the most common cell-basedtherapy applied today in the clinic.

HSC transplantation is used for the treatment of patients with acute orchronic leukemia, aplastic anemia and various immunodeficiencysyndromes, as well as various non-hematological malignancies andauto-immune disorders. For patients with hematological malignancies, HSCtransplantation may rescue patients from treatment-induced aplasia,which can occur following high-dose chemotherapy and/or radiotherapy.

Despite the widespread clinical utility of HSC transplantation, thethree major sources of HSCs (human bone marrow, mobilized peripheralblood, and umbilical cord blood) are limited as two-thirds of thepatients in need of somatic HSC transplantation lack well-matcheddonors. For example, for any given patient, there is only a 25% chancethat a sibling is a human leukocyte antigen (HLA)-identical match.

HLAs are proteins on a cell's surface that help the immune systemidentify the cells as either self (belonging to the body) or non-self(foreign or from outside the body). The HLA proteins are encoded byclusters of genes that form a region located on human chromosome 6 knownas the Major Histocompatibility Complex, or MHC, in recognition of theimportant role of the proteins encoded by the MHC loci in graftrejection. Accordingly, the HLA proteins are also referred to as MHCproteins. Although matching the MHC molecules of a transplant to thoseof the recipient significantly improves the success rate of clinicaltransplantation, it does not prevent rejection, even when the transplantis between HLA-identical siblings. Such rejection may be triggered bydifferences between the minor Histocompatibility antigens. Thesepolymorphic antigens are usually “non-self” peptides bound to MHCmolecules on the cells of the transplant tissue, and differences betweenminor Histocompatibility antigens will often cause the immune system ofa transplant recipient to eventually reject a transplant, even wherethere is a match between the MHC antigens, unless immunosuppressivedrugs are used.

There are three types each of class I and class II HLA. A person(typically a sibling) who has a class I and class II HLA match is calleda related donor. Increased survival is associated with a match betweenrecipient and donor class I HLA-A, HLA-B, HLA-C, and class II HLA-DRB1and HLA-DQB1 (Morishima, et al., 2002 Blood (99):4200-6). For a patientwho does not have a matched, related donor, a search through donor banksmay provide a person with matching HLA types. However the number ofpeople in need of a cell or tissue transplant, such as an HSCtransplant, is far greater than the available supply of cells andtissues suitable for transplantation. Under these circumstances, it isnot surprising that obtaining a good match between the MHC proteins of arecipient and those of the transplant is frequently impossible.Therefore, many transplant recipients must wait for an MHC-matchedtransplant to become available or accept a transplant that is notMHC-matched and endure higher doses of immunosuppressive drugs and stillrisk rejection. The ability to generate and manipulate HSCs, and/or toinduce tolerance in recipients of transplants, therefore, will greatlybenefit the treatment and management of human disease.

Based on work in the avian embryo, and subsequently in frogs andmammals, it has been demonstrated that the developmental programs ofblood and endothelium are closely linked. For example, endothelial andhematopoietic cells emerge concurrently and in close proximity in yolksac blood islands. The yolk sac blood islands derive from aggregates ofmesodermal cells that colonize the yolk sac. The center of theseaggregates gives rise to the embryonic hematopoietic cells whereas theperipheral population differentiates into endothelial cells which formthe vasculature that surrounds the inner blood cells. These observationssupport the notion that endothelial and hematopoietic cells have acommon precursor.

Additionally, in zebrafish and mouse embryos, both endothelial andhematopoietic lineages share the expression of certain genes, such asFlk1, Flt1, Tie1, Tie2, CD34, Scl, and Runx1 (Fina et al. 1990 Blood(75): 2417-2426; Millauer et al. 1993 Cell (72): 835-846; Yamaguchi etal. 1993 Development (118): 489-498; Anagnostou et al. 1994 PNAS USA(91): 3974-3978; Kallianpur et al. 1994 Blood (83): 1200-12081; Young etal. 1995 Blood (85): 96-105, Asahara et al. 1997 Science (275): 964-967;Kabrun et al. 1997 Development (124): 2039-2048). Likewise certain genemutations affect both endothelial and hematopoietic cell development(Shalaby et al. 1995 Nature (376): 62-66; Robb et al. 1995 PNAS USA(92): 7075-7079; Shivdasani et al. 1995 Nature (373): 432-434; Stainieret al. 1995 Development (121): 3141-3150; Bollerot et al. 2005 APMIS(113): 790-803). Further, the deletion of either Flk1 or Flt1, which areboth receptors for vascular endothelial growth factor (VEGF), results ina disruption of hematopoietic and endothelial development in the mouseembryo.

The generation of mouse hemangioblasts from mouse embryonic stem cellsin vitro has been reported in the literature (Choi et al. 1998Development 125: 727-732). Further, human precursor cells capable ofgiving rise to both hematopoietic and endothelial cells have beenderived from human ES cells (Wang et al 2004 Immunity (21): 31-41 andWang et al. J Exp Med (201): 1603-1614), but only in small quantities,hundreds of cells at best. Moreover, no method or conditions exist forthe expansion of the hemangioblast precursor cells in vitro.

Thus, there remains a need for methods for generating and expandinglarge numbers of human hemangioblasts as well as hemangioblastderivative cell types, i.e., hematopoietic and endothelial cells, andall solutions/mixtures containing such quantities of hemangioblasts orderivative cell types. Such methods would increase the availability ofcells for transplantation as well as have utility in a variety of othertherapeutic applications, such as in induction of immunologicaltolerance.

There is additionally a critical need for available blood fortransfusion. The Red Cross and other suppliers of blood report a nearconstant shortage of blood. This is especially true for patients withunique blood types, patients who are Rh+, or following accidents ordisasters resulting in mass casualties. Additionally, in times of war,the military has an acute need for available blood for use in thetreatment of traumatic war-related injuries. The present inventionprovides differentiated hematopoietic cells for use in blood banking andtransfusion. The cells and methods of the present invention will providea safe and reliable advance beyond the traditional reliance on blooddonations, and will help prevent critical shortages in available blood.

SUMMARY OF THE INVENTION

The present invention overcomes the problems described above byproviding a method of generating and expanding human hemangioblasts orhemangio-colony forming cells in vitro. The ability to expand humanhemangioblasts or hemangio-colony forming cells by the novel methodsdisclosed herein allows the production of cells that can be used invarious therapeutic applications. Additionally, the present inventionprovides methods for generating human hemangioblast or hemangio-colonyforming lineage cells (i.e., hematopoietic and endothelial cells) thatmay be used in therapeutic applications. The methods of the inventionprovide further utility in that they enable the generation of largenumbers of human hemangioblasts or hemangio-colony forming cells as wellas hematopoietic and endothelial cells, and cells differentiatedtherefrom, that may be used at commercial scale.

The present invention provides for a method for generating and expandinghuman hemangio-colony forming cells in vitro, said method comprising thesteps of:

a) culturing a cell culture comprising human embryo-derived cells inserum-free media in the presence of at least one growth factor in anamount sufficient to induce the differentiation of said embryo-derivedcells into embryoid bodies; and

(b) adding at least one growth factor to said culture comprisingembryoid bodies and continuing to culture said culture in serum-freemedia, wherein said growth factor is in an amount sufficient to expandhuman hemangio-colony forming cells in said embryoid bodies culture,

wherein said stem cells, embryoid bodies and hemangio-colony formingcells are grown in serum-free media throughout steps (a) and (b) of saidmethod.

This invention also provides a method for generating and expanding humanhemangio-colony forming cells in vitro, said method comprising the stepsof:

(a) culturing a cell culture comprising human embryo-derived cells inserum-free media in the presence of at least one growth factor in anamount sufficient to induce the differentiation of said embryo-derivedcells into embryoid bodies;

(b) adding at least one growth factor to said culture comprisingembryoid bodies and continuing to culture said culture in serum-freemedia, wherein said growth factor is in an amount sufficient to expandhuman hemangio-colony forming cells in said embryoid bodies culture,

(c) said embryoid bodies are disaggregated into single cells;

(d) adding at least one growth factor to said culture comprising saidsingle cells and continuing to culture said culture in serum-free media,wherein said growth factor is in an amount sufficient to expand humanhemangio-colony forming cells in said culture comprising said singlecells,

wherein said stem cells, embryoid bodies and hemangio-colony formingcells are grown in serum-free media throughout steps (a)-(d) of saidmethod.

In certain embodiments of the invention, the embryo-derived cell is anembryonic stem cell.

In certain embodiments of the methods for generating and expanding humanhemangio-colony forming cells of this invention, the growth factor is aprotein that comprises a homeobox protein, or a functional variant or anactive fragment thereof. In certain embodiments, the homeobox protein isa protein that comprises HOXB4, or a functional variant or an activefragment thereof. It is contemplated that the HOXB4 could be mammalianHOXB4, including mouse and human HOXB4. The HOXB4 protein could be fulllength HOXB4 protein. In yet further embodiments, the HOXB4 comprisesthe amino acid sequence of SEQ ID NO: 1 or SEQ ID NO: 4.

In certain embodiments of the methods for generating and expanding humanhemangio-colony forming cells of this invention, the growth factor thatcomprises HOXB4 is a fusion protein that comprises HOXB4 and a proteintransduction domain (PTD). In yet further embodiments, the PTD and theHOXB4 are conjugated via a linker. In yet further embodiments, the PTDis TAT protein, a functional variant or an active fragment thereof(including a TAT polypeptide). In certain embodiments, the TAT proteincomprises the amino acid sequence of SEQ ID NO: 14. In yet furtherembodiments, the PTD comprises one or more copies of a TAT polypeptidewith the amino acid sequence of SEQ ID NO: 14. In certain embodiments,the PTD is SEQ ID NO: 15.

In certain embodiments of the methods for generating and expanding humanhemangio-colony forming cells of this invention, the growth factor isselected from the group consisting of vascular endothelial growth factor(VEGF), bone morphogenic proteins (BMP), stem cell factor (SCF), Flt-3L(FL) thrombopoietin (TPO) and erythropoietin (EPO). In furtherembodiments, vascular endothelial growth factor (VEGF) or bonemorphogenic protein (BMP), or both, are added to culturing step (a)within 0-48 hours of culturing the cell culture comprising the hEScells. In still other further embodiments, the stem cell factor (SCF),Flt-3L (FL) or thrombopoietin (TPO), or any combination thereof, areadded to the cell culture comprising hES cells within 48-72 hours fromthe start of culturing step (a).

In certain embodiments of the methods for generating and expanding humanhemangio-colony forming cells of this invention, a growth factor thatcomprises a HOXB4 protein, or a functional variant or active fragment(or domain) thereof, is added to the step(s) in which said protein isadded multiple times, such as, for example, once a day or once everyother day.

In certain embodiments of the methods for generating and expanding humanhemangio-colony forming cells of this invention, the growth factorcomprising a homeobox protein is added to step (b) within 48-72 hoursfrom the start of step (a). In certain embodiments of the methods ofthis invention, the HOXB4 protein, or functional variants or activefragments thereof, is added to step (b) within 48-72 hours from thestart of step (a).

In certain embodiments, the methods for generating and expanding humanhemangio-colony forming cells of this invention further comprise thestep of adding erythropoietin (EPO) to step (b). In certain embodiments,the method of this invention described in paragraph 0016 furthercomprises the step of adding erythropoietin (EPO) to steps (b) and (d).

In certain embodiments, the methods for generating and expanding humanhemangio-colony forming cells of this invention further comprise thestep(s) of purifying and/or isolating the human hemangio-colony formingcells. The hemangio-colony forming cells may be purified by usingimmunoaffinity column chromatography with an anti-CD71 antibody. Thehemangio-colony forming cells may be isolated by size and/or bymorphology.

In certain embodiments of the methods for generating and expanding humanhemangio-colony forming cells of this invention, the cell culturecomprising human embryo-derived stem cells are derived from a library ofhuman embryonic stem cells, wherein said library of human embryonic stemcells comprises stem cells, each of which is hemizygous or homozygousfor at least one MHC allele present in a human population, wherein eachmember of said library of stem cells is hemizygous or homozygous for adifferent set of MHC alleles relative to the remaining members of thelibrary. In further embodiments, the library of human embryonic stemcells comprises stem cells that are hemizygous or homozygous for all MHCalleles present in a human population. These methods generate a libraryof human hemangio-colony forming cells, each of which is hemizygous orhomozygous for at least one MHC allele present in a human population,wherein each member of said library of stem cells is hemizygous orhomozygous for a different set of MHC alleles relative to the remainingmembers of the library. In further embodiments, these methods generate alibrary of human hemangio-colony forming cells that are hemizygous orhomozygous for all MHC alleles present in a human population. Thus, thisinvention also provides a library of human hemangio-colony forming cellsmade by such methods. This library could be used as follows.

This invention provides a method to treat a human patient in need oftreatment involving administering human hematopoietic stem cells orhuman endothelial cells to said patient, comprising the steps of:

(a) selecting said patient;

(b) identifying MHC proteins expressed on the surface of said patient'scells;

(c) providing a library of human hemangio-colony forming cells describedin the preceding paragraph 0024;

(d) selecting the human hemangio-colony forming cells from the librarythat match said patient's MHC proteins on said patients' cells;

(e) differentiating said human hemangio-colony forming cells identifiedin step (d) into human hematopoietic stem cells, endothelial cells orboth, depending on need;

(f) administering said human hematopoietic stem cells, endothelial cellsor both from step (e) to said patient. This method could be performed ina regional center, such as a hospital or a medical center, or any othersuitable facility.

In certain embodiments, the methods for generating and expanding humanhemangio-colony forming cells of this invention further comprise thestep of growing the human hemangio-colony forming cells under conditionssuitable to induce the differentiation of said human hemangio-colonyforming cells into human hematopoietic stem cells.

In certain embodiments, the methods for generating and expanding humanhemangio-colony forming cells of this invention further comprise thestep of growing said human hemangio-colony forming cells underconditions suitable to induce the differentiation of said humanhemangio-colony forming cells into human endothelial cells. In furtherembodiments, the condition suitable to induce the differentiation ofsaid human hemangio-colony forming cells into human endothelial cellscomprises growing the human hemangio-colony forming cells onfibronectin-coated culture plates.

In certain embodiments of this invention, the methods for generating andexpanding human hemangio-colony forming cells result in at least 10,000human hemangio-colony forming cells, at least 50,000 humanhemangio-colony forming cells, at least 100,000 human hemangio-colonyforming cells, at least 500,000 human hemangio-colony forming cells, atleast 1×10⁶ human hemangio-colony forming cells, at least 2×10⁶ humanhemangio-colony forming cells, at least 3×10⁶ human hemangio-colonyforming cells or at least 4×10⁶ human hemangio-colony forming cells.These methods result in cell solutions that may comprise between 10,000to 4 million human hemangio-colony forming cells.

Thus, this invention also provides a solution of human hemangio-colonyforming cells (which could be grown in serum-free media) comprising atleast 10,000 human hemangio-colony forming cells, at least 50,000 humanhemangio-colony forming cells, at least 100,000 human hemangio-colonyforming cells, at least 500,000 human hemangio-colony forming cells, atleast 1×10⁶ human hemangio-colony forming cells, at least 2×10⁶ humanhemangio-colony forming cells, at least 3×10⁶ human hemangio-colonyforming cells or at least 4×10⁶ human hemangio-colony forming cells.These solutions could be injectable to a subject. These solutions couldbe suitable for freezing. These solutions could be serum-free. The humanhemangio-colony forming cells in these solutions are capable ofdifferentiating into at least hematopoietic and endothelial cells buthave greater developmental potential to differentiate into other celltypes. This invention also provides a use of these solutions for themanufacture of a medicament to treat a disease that could be treated bythe administration of hemangio-colony forming cells, hematopoietic cellsor endothelial cells.

This invention also provides a method of producing a solution of humanhemangio-colony forming cells suitable for injection into a patientcomprising the steps of isolating the solution of cells described in thepreceding paragraph and placing the cells into a solution suitable forinjection into a patient. This invention also provides a method ofproducing a solution of human hemangio-colony forming cells suitable forfreezing comprising the steps of isolating the solution of cellsdescribed in the preceding paragraph and placing the cells into asolution suitable for freezing.

This invention also provides a method for administering humanhematopoietic stem cells to a patient in need thereof, comprising thesteps of:

(a) selecting a patient in need thereof;

(b) supplying human hemangio-colony forming cells generated and expandedby a method of this invention;

(c) differentiating said human hemangio-colony forming cells into humanhematopoietic stem cells; and

(d) administering some of all of said human hematopoietic stem cells tosaid patient.

This invention also provides a method for administering humanhematopoietic stem cells to a patient in need thereof, comprising thesteps of:

(a) selecting the patient in need thereof;

(b) supplying human hemangio-colony forming cells in an amount of atleast 10,000 cells;

(c) differentiating said human hemangio-colony forming cells into humanhematopoietic stem cells; and

(d) administering some or all of said human hematopoietic stem cells tosaid patient.

This invention also provides a method for administering humanendothelial cells into a patient in need thereof, comprising the stepsof:

(a) selecting a patient in need thereof;

(b) supplying human hemangio-colony forming cells generated and expandedby a method of this invention;

(c) differentiating said human hemangio-colony forming cells into humanendothelial cells; and

(d) administering some or all of said human endothelial cells to saidpatient.

This invention also provides a method for administering humanendothelial cells into a patient in need thereof, comprising the stepsof:

(a) selecting a patient in need thereof;

(b) supplying human hemangio-colony forming cells in an amount of atleast 10,000 cells;

(c) differentiating said human hemangio-colony forming cells into humanendothelial cells; and

(d) administering some or all of said human endothelial cells to saidpatient.

In certain embodiments, the human hemangio-colony forming cells are inan amount between 10,000 to 4 million cells.

This invention also provides a method for treating an endothelial celldisorder in a patient in need thereof, comprising the steps of:

(a) selecting a patient in need thereof;

(b) supplying human hemangio-colony forming cells generated and expandedby a method described above;

(c) differentiating said human hemangio-colony forming cells into humanendothelial cells; and

(d) administering some or all of said human endothelial cells to saidpatient.

This invention also provides a method for treating an endothelial celldisorder in a patient in need thereof, comprising the steps of:

(a) selecting a patient in need thereof;

(b) supplying human hemangio-colony forming cells in an amount of atleast 10,000 cells;

(c) differentiating said human hemangio-colony forming cells into humanendothelial cells; and

(d) administering some or all of said human endothelial cells to saidpatient.

In certain embodiments, the human hemangio-colony forming cells are inan amount between 10,000 to 4 million cells.

The endothelial cell disorder to be treated by these methods includesmyocardium infarction, stroke, atherosclerosis and ischemia. Theischemia could occur in the brain, limbs, heart, lungs, skin and eye.

This invention provides a method for producing human hematopoietic stemcells in vitro, comprising the steps of:

(a) supplying human hemangio-colony forming cells generated and expandedby a method of this invention; and

(b) growing said human hemangio-colony forming cells under conditionssuitable to induce the differentiation of said human hemangio-colonyforming cells into human hematopoietic stem cells.

This invention also provides a method for producing human endothelialcells in vitro, comprising the steps of:

(a) supplying human hemangio-colony forming cells generated and expandedby a method of this invention; and

(b) growing said human hemangio-colony forming cells under conditionssuitable to induce the differentiation of said human hemangio-colonyforming cells into human endothelial cells.

This invention also provides a method for expanding hemangio-colonyforming cells comprising growing mammalian hemangio-colony forming cellsin serum-free media in the presence of a protein that comprises ahomeobox protein (such as HOXB4) or a functional equivalent or an activefragment thereof in an amount sufficient to support the proliferation ofsaid hemangioblast cells. The hemangio-colony forming cells to beexpanded could be enriched, purified, or isolated from cord blood,peripheral blood, or bone marrow. The hemangio-colony forming cellscould be human hemangio-colony forming cells. This method could resultin solutions comprising hemangio-colony forming cells of between 10,000to 4×10⁶ hemangio-colony forming cells, or more. The HOXB4 protein usedfor this method could be any that are suitable for use for the methodsfor generating and expanding human hemangio-colony forming cells of thisinvention.

The present invention also provides for methods of inducingimmunological tolerance using the human hemangio-colony forming cellsgenerated and expanded or expanded according to the methods of thisinvention. The tolerizing human hemangio-colony forming cells are chosento share histocompatibility markers with an allograft, and may beadministered to a human recipient before or concurrently with theallograft or cell treatment that regenerates a cellular function neededby the patient. The resulting immune tolerance subsequently decreasesthe risk of acute or chronic rejection of the allograft or celltreatment.

The large numbers of hemangio-colony forming cells generated by themethods disclosed herein enable tolerance protocols in which toxicpre-conditioning treatments may be eliminated. The donor humanhemangio-colony forming cells may be administered to a human recipientprior to implantation of a graft or implantation of an organ, tissue, orcells that are matched with respect to the donor hemangio-colony formingcells. The human hemangio-colony forming cells and graft may be obtainedfrom the same donor. The graft may be derived from differentiated donorhuman hemangio-colony forming cells. The human hemangio-colony formingcells and graft may alternatively be obtained from different donorswherein the donors are matched. The human hemangio-colony forming cellsmay be administered to human recipients to induce tolerance inrecipients in need thereof.

In certain embodiments, the present invention relates to a method ofinducing tolerance in a human recipient to a donor allograft, whereinthe method comprises the steps of (a) administering to the recipient anagent that inhibits T cell co-stimulation (b) introducing into therecipient human hemangio-colony forming cells that are generated andexpanded, or expanded, according to the methods described herein, and(c) implanting the allograft into the recipient. The humanhemangio-colony forming cells (donor cells) promote acceptance of theallograft by the recipient. In certain embodiments, an agent thatinhibits T cell costimulation is an agent that inhibits or blocks theCD40 ligand-CD40 costimulatory interaction. The method may furthercomprise administering an agent that inhibits the CD28-B7 interaction.The method may or may not comprise thymic irradiation and/or T celldepletion or inactivation. The aforementioned method may also producemixed chimerism in the absence of hematopoietic space created by wholebody irradiation.

The invention also provides for a method of promoting tolerance in ahuman recipient to a donor allograft, wherein the method comprises thesteps of (a) creating thymic space in said recipient; (b) depleting orinactivating donor-reactive T cells in said recipient; (c) introducingdonor human hemangio-colony forming cells of said donor or that arematched to said donor into said recipient; and (d) implanting saidallograft into said recipient, wherein the donor hemangio-colony formingcells induce tolerance to the allograft. In certain embodiments, themethod does not comprise hematopoietic space-creating irradiation. Themethod may comprise creating thymic space by administering to therecipient at least one treatment selected from among thymic irradiation(which can be fractionated), steroids, corticosteroids, brequinar, or animmune suppressant or drug.

The invention also provides methods for generating cells suitable foruse in blood transfusion. For example, the invention provides methodsfor generating red blood cells that can be used in transfusion. As such,the present invention provides a solution to help alleviate the chronicshortage of blood available for donation.

In certain embodiments, the present invention provides a method forproducing differentiated hematopoietic cells from human hemangio-colonyforming cells in vitro, said method comprising the steps of:

(a) providing human hemangio-colony forming cells; and

(b) differentiating said hemangio-colony forming cells intodifferentiated hematopoietic cells.

In certain embodiments, the present invention provides a method forperforming blood transfusions using hematopoietic cells differentiatedin vitro from human hemangio-colony forming cells, said methodcomprising the steps of:

(a) providing human hemangio-colony forming cells;

(b) differentiating said hemangio-colony forming cells intodifferentiated hematopoietic cells; and

(c) performing blood transfusions with said differentiated hematopoieticcells.

In certain embodiments, said hemangio-colony forming cells are recoveredfrom frozen cultures.

In certain embodiments, the present invention provides a method forperforming blood transfusions using hematopoietic cells differentiatedin vitro from human hemangio-colony forming cells, said methodcomprising the steps of:

(a) culturing a cell culture comprising human embryo-derived cells inthe presence of at least one growth factor in an amount sufficient toinduce the differentiation of said embryo-derived cells into embryoidbodies;

(b) adding at least one growth factor to said culture comprisingembryoid bodies, wherein said growth factor is in an amount sufficientto expand human hemangio-colony forming cells in said embryoid bodiesculture;

(c) differentiating said hemangio-colony forming cells intodifferentiated hematopoietic cells; and

(d) performing blood transfusions with said differentiated hematopoieticcells.

In certain embodiments, said embryo-derived cells, embryoid bodies andhemangio-colony forming cells are grown in serum-free media throughoutstep (a) of said method.

In certain embodiments, the embryo-derived cell is an embryonic stemcell.

In certain embodiments, the present invention provides a method forperforming blood transfusions using hematopoietic cells differentiatedin vitro from human hemangio-colony forming cells, said methodcomprising the steps of:

(a) culturing a cell culture comprising human embryo-derived cells inthe presence of at least one growth factor in an amount sufficient toinduce the differentiation of said embryo-derived cells into embryoidbodies;

(b) adding at least one growth factor to said culture comprisingembryoid bodies, wherein said growth factor is in an amount sufficientto expand human hemangio-colony forming cells in said embryoid bodiesculture;

(c) differentiating said hemangio-colony forming cells intodifferentiated hematopoietic cells; and

(d) performing blood transfusions with said differentiated hematopoieticcells.

In certain embodiments, said stem cells, embryoid bodies andhemangio-colony forming cells are grown in serum-free media throughoutsteps (a) and (b) of said method.

In certain embodiments of the invention, the embryo-derived cell is anembryonic stem cell.

In certain embodiments, said hemangio-colony forming cells are recoveredfrom frozen cultures.

In certain embodiments, the present invention provides a method forperforming blood transfusions using hematopoietic cells differentiatedin vitro from human hemangio-colony forming cells, said methodcomprising the steps of:

(a) culturing a cell culture comprising human embryo-derived cells inthe presence of at least one growth factor in an amount sufficient toinduce the differentiation of said embryo-derived cells into embryoidbodies;

(b) adding at least one growth factor to said culture comprisingembryoid bodies, wherein said growth factor is in an amount sufficientto expand human hemangio-colony forming cells in said embryoid bodiesculture;

(c) disaggregating said embryoid bodies into single cells;

(d) adding at least one growth factor to said culture comprising saidsingle cells, wherein said growth factor is in an amount sufficient toexpand human hemangio-colony forming cells in said culture comprisingsaid single cells;

(e) differentiating said hemangio-colony forming cells intodifferentiated hematopoietic cells; and

(f) performing blood transfusions with said differentiated hematopoieticcells.

In certain embodiments, said stem cells, embryoid bodies andhemangio-colony forming cells are grown in serum-free media throughoutsteps (a)-(d) of said method.

In certain embodiments of the invention, the embryo-derived cell is anembryonic stem cell.

In certain embodiments, the growth factor is a protein that comprises ahomeobox protein, or a functional variant or an active fragment thereof.In certain embodiments, the homeobox protein comprises a HOXB4 protein,or a functional variant or an active variant thereof.

In certain embodiments, the differentiated hematopoietic cells areproduced as a single cell type. In certain embodiments, the single celltype is selected from: red blood cells, platelets, or phagocytes. Incertain embodiments, the phagocyte is selected from: granulocytes:neutrophils, basophils, eosinophils, lymphocytes or monocytes. Incertain embodiments, wherein the red blood cells express hemoglobin F.In certain embodiments, the single cell types are mixed to approximatelyequal the proportion of differentiated cell types that is found inblood, wherein the proportion of differentiated cell types that is foundin blood is 96% red blood cells, 1% platelets, and 3% phagocytes.

In certain embodiments, multiple differentiated hematopoietic cell typesare produced in the same step. In certain embodiments, the multipledifferentiated hematopoietic cell types are selected from: red bloodcells, platelets, or phagocytes. In certain embodiments, the phagocyteis selected from: granulocytes: neutrophils, basophils, eosinophils,lymphocytes or monocytes. In certain embodiments, the red blood cellsexpress hemoglobin F. In certain embodiments, the multipledifferentiated hematopoietic cell types are produced in a proportionapproximately equal to the proportion of differentiated hematopoieticcell types found in blood, wherein the proportion of differentiated celltypes that is found in blood is 96% red blood cells, 1% platelets, and3% phagocytes.

In certain embodiments, plasma is added to the differentiatedhematopoietic cells before transfusion.

In certain embodiments, the hemangio-colony forming cells are matched toa patient to ensure that differentiated hematopoietic cells of thepatient's own blood type are produced. In certain embodiments, thehemangio-colony forming cells are negative for antigenic factors A, B,Rh, or any combination thereof. In certain embodiments, thedifferentiated hematopoietic cells are red blood cells, and wherein astep of differentiating the red blood cells includes erythropoietin(EPO).

The invention also provides a human hemangio-colony forming cell, whichcell can differentiate to produce at least hematopoietic or endothelialcell types, wherein the human hemangio-colony forming cell is looselyadherent to other human hemangio-colony forming cells.

In certain embodiments, the invention provides a human hemangio-colonyforming cell, which cell can differentiate to produce at leasthematopoietic and endothelial cell types, wherein the humanhemangio-colony forming cell is loosely adherent to other humanhemangio-colony forming cells.

In certain embodiments, the invention provides a human hemangio-colonyforming cell, which cell can differentiate to produce at leasthematopoietic and endothelial cell types, wherein the humanhemangio-colony forming cell is loosely adherent to other humanhemangio-colony forming cells, and wherein the human hemangio-colonyforming cell does not express CD34 protein.

In certain embodiments, the invention provides a human hemangio-colonyforming cell, which cell can differentiate to produce at leasthematopoietic and endothelial cell types, wherein the humanhemangio-colony forming cell does not express any of the followingproteins: CD34, CD31, KDR, and CD133.

In certain embodiments, the invention provides a cell culture comprisinghuman hemangio-colony forming cells, which cells can differentiate toproduce at least hematopoietic or endothelial cell types, wherein thehemangio-colony forming cells are loosely adherent to each other.

In certain embodiments, the invention provides a cell culture comprisinghuman hemangio-colony forming cells, which cells can differentiate toproduce at least hematopoietic and endothelial cell types, wherein thehemangio-colony forming cells are loosely adherent to each other.

In certain embodiments, the invention provides a cell culture comprisinga substantially purified population of human hemangio-colony formingcells, which cells can differentiate to produce at least hematopoieticand endothelial cell types, wherein the hemangio-colony forming cellsare loosely adherent to each other, and wherein the hemangio-colonyforming cells do not express CD34 protein.

In certain embodiments, the invention provides a cell culture comprisinghuman hemangio-colony forming cells differentiated from embryo-derivedcells, wherein the hemangio-colony forming cells are loosely adherent toeach other.

In certain embodiments, the cell culture comprises at least 1×10⁶ humanhemangio-colony forming cells. In certain embodiments, the cell culturecomprises at least 5×10⁶ human hemangio-colony forming cells.

In certain embodiments, the embryo-derived cell is an embryonic stemcell line. In certain embodiments, the embryo-derived cell is selectedfrom an embryo, a blastomere, a blastocyst, or an inner cell mass.

In certain embodiments, the invention provides a pharmaceuticalpreparation comprising human hemangio-colony forming cells, which cellscan differentiate to produce at least hematopoietic or endothelial celltypes, wherein the hemangio-colony forming cells are loosely adherent toeach other.

In certain embodiments, the invention provides a pharmaceuticalpreparation comprising human hemangio-colony forming cells, which cellscan differentiate to produce at least hematopoietic and endothelial celltypes, wherein the hemangio-colony forming cells are loosely adherent toeach other.

In certain embodiments, the invention provides a pharmaceuticalpreparation comprising human hemangio-colony forming cells, which cellscan differentiate to produce at least hematopoietic and endothelial celltypes, wherein the hemangio-colony forming cells do not express any ofthe following proteins: CD34, CD31, KDR, and CD133.

In certain embodiments, the pharmaceutical preparation comprises atleast 1×10⁶ human hemangio-colony forming cells. In certain embodiments,the preparation comprises at least 5×10⁶ human hemangio-colony formingcells.

In certain embodiments, the pharmaceutical preparation comprisinghemangio-colony forming cells are differentiated from embryo-derivedcells. In certain embodiments, the embryo-derived cell is an embryonicstem cell. In certain embodiments, the embryo-derived cell is selectedfrom an embryo, a blastomere, a blastocyst, or an inner cell mass.

In certain embodiments, the invention provides a cryopreservedpreparation of the hemangio-colony forming cells described in any of thepreceding paragraphs.

In certain embodiments, the invention provides a cryopreservedpreparation of at least 1×10⁶ human hemangio-colony forming cells,wherein the hemangio-colony forming cells do not express any of thefollowing proteins: CD34, CD31, KDR, and CD133.

In certain embodiments, the cryopreserved preparation comprises at least5×10⁶ human hemangio-colony forming cells.

In certain embodiments, the cryopreserved preparation comprising humanhemangio-colony forming cells do not express CD34 protein. In certainembodiments, the cryopreserved preparation comprising humanhemangio-colony forming cells do not express CD34, CD31, CD133, and KDRproteins. In certain embodiments, the cryopreserved preparationcomprising human hemangio-colony forming cells express LMO2 and GATA2proteins.

In certain embodiments, the invention provides a culture comprising ahematopoietic cell differentiated from the hemangio-colony forming cellsas described above.

In certain embodiments, the invention provides a culture comprising anendothelial cell differentiated from the hemangio-colony forming cellsas described above.

In certain embodiments, the invention provides a culture comprising asmooth muscle cell differentiated from the hemangio-colony forming cellsas described above.

In certain embodiments, the invention provides a culture comprising acardiomyocyte differentiated from the hemangio-colony forming cells asdescribed above.

In certain embodiments, the invention provides for the use of the humanhemangio-colony forming cells as described above in the manufacture of amedicament to treat a condition in a patient in need thereof.

In certain embodiments, the invention provides the use of the cellculture as described above in the manufacture of a medicament to treat acondition in a patient in need thereof.

In certain embodiments, the invention provides the use of thepharmaceutical preparation as described above in the manufacture of amedicament to treat a condition in a patient in need thereof.

The invention contemplates combinations of any of the foregoing aspectsand embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the hematopoietic CFUs derived from hemangioblastsgenerated from H1-GFP ES cells.

FIG. 2 illustrates the cell morphology of the erythroid colony formingunits (CFU-E) cultured in serum-free (Stemline) culture media.

FIG. 3 illustrates the cell morphology of the multipotent colony formingunits (CFU-GEMM/Mix) cultured in serum-free (Stemline) culture media.

FIG. 4 illustrates the cell morphology of the multipotent colony formingunits (CFU-GEMM/Mix) cultured in serum-free (Stemline) culture media.

FIG. 5 illustrates the cell morphology of the granulocyte colony formingunits (CFU-G) and macrophage colony forming units (CFU-M) cultured inserum-free (Stemline) culture media.

FIG. 6 illustrates the cell morphology of the granulocyte/macrophagecolony forming units (CFU-GM) and megakaryotcye macrophage colonyforming units (CFU-Mk) cultured in serum-free (Stemline) culture media.

FIGS. 7a-7b illustrate formation of tube-cord structures following thereplating of hemangioblasts derived from 7 a H9 ES cells and 7 b ACT30ES cells on Matrigel-based medium.

FIG. 8 illustrates the tube-cord structure of hemangioblasts generatedfrom H1-GFP ES cells that were cultured on fibronectin-coated plates inEGM-2 media and then on Matrigel, as described in Example 2. FIG. 8 alsoillustrates the uptake of Ac-LDL by the cells when incubated with Alexafluor labeled Ac-LDL, as described in Example 2. The middle top andright top panels show phase contrast pictures.

FIG. 9 illustrates the expression of von Willebrand factor (vWF) (lightgray staining) in hemangioblasts generated from H1-GFP ES cells thatwere cultured on fibronectin-coated plates in EGM-2 media, as describedin Example 2.

FIG. 10 illustrates the formation of vessels in cross-sections ofhaematoxylin and eosin (H&E)-stained Matrigel plugs that were injectedinto SCID mice, as described in Example 4.

FIG. 11 illustrates that the vessels from the cross-sections of Matrigelplugs are cells derived from human hemangioblasts, as indicated by thepositive staining for human specific nuclei antibody (light graystaining), as described in Example 4.

FIG. 12 illustrates the mRNA sequence of human HOXB4 (Accession No.NM_024015.4; GI: 85376187) (SEQ ID NO: 2).

FIG. 13 illustrates the amino acid sequence of human HOXB4 (AccessionNo. NP_076920.1; GI: 13273315) (SEQ ID NO: 1).

FIG. 14 illustrates the mRNA sequence of human HOXB4 (Accession No.BC049204.1; GI:29351567) (SEQ ID NO: 4).

FIG. 15 illustrates the amino acid sequence of human HOXB4 (AccessionNo. AAH49204.1; GI:29351568) (SEQ ID NO: 3).

FIGS. 16a-16v illustrate the phenotypic characterization ofhemangioblasts (BL-CFC) derived from human ES cells: 16 a hemangioblastcolony or blast colony (BL-CFC or BC, ×400); 16 b Secondary EBs (×400);16 c Blast cells (hES-BC cells) with Wright-Giemsa staining (×1000); 16d-16 f: GATA-1 staining; 16 d blast cells stained with GATA-1 (×600) and16 e GATA-1 and DAPI; 16 f BM cells stained with GATA-1 and DAPI (×400).16 g-16 i: LMO2 staining; 16 g blast cells stained with LMO2 (×600) and16 h LMO2 and DAPI (×600); 16 i K562 cells stained with LMO2 and DAPI(×1000); 16 j-16 m: CD71 staining (bright or light gray); 16 j blastcells stained with CD71(×600) and 16 k CD71 and DAPI (×600); 16 m BMcells stained with CD71 and DAPI (×1000); 16 n-16 p: CXCR-4 staining(bright or light gray); 16 n blast cells stained with CXCR-4 (×600) and16 o CXCR- and DAPI (×600); 16 p BM cells stained with CXCR-4 and DAPI(×600); 16 q-16 s Epo-receptor staining (medium gray); 16 q blast cellsstained with Epo-receptor (×600) and 16 r Epo-receptor and DAPI (×600);16 s BM cells stained with Epo-receptor and DAPI (×600); 16 t-16 vTpo-receptor staining (medium gray); 16 t blast cells stained withTpo-receptor (×600) and 16 u Tpo-receptor and DAPI (×600); 16 v BM cellsstained with Tpo-receptor and DAPI (×1000), as described in Examples 1and 2. Note: hES-BC (hemangioblast) cells in panels 16 d and 16 n weredouble stained with GATA-1 and CXCR-4 antibodies, but presentedseparately; hES-BC (hemangioblast) cells in panels 16 q and 16 t werealso double stained with Epo-receptor and Tpo-receptor antibodies andpresented separately.

FIG. 17a -17 cc illustrates the functional characterization ofhemangioblasts (BL-CFC or blast cells) derived from human ES cells invitro: 17 a-17 d Hematopoietic CFUs derived from purifiedhemangioblasts: 17 a CFU-erythroid (×100); 17 b CFU-granulocyte (×100);17 c CFU-macrophage; and 17 d CFU-multilineage (mix, ×100); 17 e-17 hWright-Giemsa staining of CFU-cells: 17 e erythroid (×1000); 17 fgranulocyte (×1000); 17 g macrophage (×400) and 17 h, mix (×1000). 17i-17 k Immunostaining of CFU cells: 17 i CFU-erythroid cells stainedwith CD235a (arrows, ×1000); 17 j CFU-granulocyte cells stained withCD13 (arrows, ×1000) and 16 k CFU-mix cells stained with CD45 (arrows,×1000). 17 m-17 p and 17 v-17 y FACS analysis of pooled CFU cells: 17 mmouse IgG isotype control; 17 n CD45; 17 o CD13 and 17 p CD235; 17 vmouse IgG isotype controls; 17 w CD45 and CD235a; 17 x CD13 and CD45;and 17 y CD13 and CD235a. 17 q-17 u and 17 z-17 cc Endothelial cellsderived from purified hemangioblasts, or blast cells or hES-BC cells: 17q Capillary tube-like structures formed on Matrigel after platingadherent cells derived from hemangioblasts (×100); 17 r Ac-LDL uptake(gray) by endothelial cells derived from hemangioblasts (×200); 17 sExpression of vWF (arrows) in hemangioblast-derived endothelial cells,nuclei were stained with DAPI (×600); 17 t Localization of PEC AMI(bright staining) in hemangioblast-derived endothelial cells, nuclei(round features in the figure) were stained with DAPI (×200); 17 uLocalization of VE-cadherin (arrows) in hemangioblast-derivedendothelial cells, nuclei (round features) were stained with DAPI(×200). 17 z Ac-LDL update (arrow heads) and vWF expression (arrows,×600); 17 aa uptake of Ac-LDL (arrow heads) and expression ofVE-candherin (arrows, ×600); 17 bb expression of vWF (arrows) and CD31(arrow heads, ×600); 17 cc expression of VE-candherin (arrows) and CD31(arrow heads, ×600). See Example 2.

FIGS. 18a-18m show the clonogenicity of blast colonies derived from hEScells. 18 a-18 c: Clonogenicity of blast colonies. 18 a and 18 b, twoblast colonies developed in a mixture of WA01-GFP and MA01 EBs, whichdemonstrated the clonal origin of the blast colonies; 18 a phase image(×100); 18 b GFP image (×100); 18 c blast colony developed from a singlecell (×400). 18 d and 18 e: Expansion of single blast colony in liquidculture, both hematopoietic and endothelial lineages were observed(×200). 18 d, ×200 18 e, ×400; 18 f-18 h: Endothelial cells derived froma single BC: 18 f Capillary tube-like structures formed on Matrigelafter plating adherent cells derived from a single BC (×100); 18 gAc-LDL uptake (arrows) by endothelial cells derived from a single BC,nuclei were stained with DAPI (×400); 18 h Expression of vWF (arrows) ina single BC-derived endothelial cells, nuclei were stained with DAPI(×400). 18 i-18 m: Hematopoietic CFUs derived from a single BC: 18 iCFU-erythroid (×100); 18 j CFU-granulocyte (×100); 18 k CFU-macrophage(×100); and 18 l CFU-multilineage (mix, ×100). 18 m The gel shows theresults of a PCR analysis of GFP sequences in GFP+ and GFP-hES-BCs(hemangioblast) derived from plating mixtures of WA01-GFP+ andMA01-GFP-cells. Lanes: WA01-GFP+, parental WA01/GFP+hES cells;MA01-GFP-, parental MA01 hES cells; H₂O, water negative control;BC-GFP+, GFP positive BC picked up from cell-mixing plating; 1-10, GFPnegative BCs picked up from cell-mixing plating. A myogenin gene wasused for a PCR reaction control. See Example 2.

FIGS. 19a-19c provide a characterization of a tPTD-HOXB4 fusion protein.19 a 6×His-fused tPTD-HOXB4 recombinant protein was expressed in E. coliand purified by nickel ProBand resins. Two batches (designated as (1)and (2)) of desalted tPTD-HOXB4 protein was examined for its purity andconcentration by SDS-PAGE gel. 19 b tPTD-HOXB4 protein is unstable inmedium with 5% FBS but 19 c retains its integrity in serum free mediumwith live ES cells (N=stemline II medium only; h=hours).

FIGS. 20a-20f illustrate the robust repair of ischemic retinalvasculature after systematic injection with hES-derived hemangioblasts.Retinal ischemia was induced by 2 h of hydrostatic pressure on theanterior chamber of mouse eyes. Seven days later fluorescently labeled(GFP+) hemangioblasts were injected either intravitreally orintravenously. One day later the animals were euthanized. Eyes wereenucleated, dissected, and the retinas were mounted flat and imaged bylaser scanning confocal microscopy or sectioned for imaging. 20 a amerge from a typical control (uninjured) eye showing typical retinalvascular anatomy with no background green fluorescence; separateGFP+(bottom inset) and GFP− (top inset) channels are also shown; 20 b amerge from the treated eye of the same animal showing fluorescentlylabeled (GFP+) hemangioblast-derived cells (bright areas of thevasculature) incorporated into the ischemic vasculature; separate green(GFP+ hemangioblasts, bottom inset) and unlabeled cells (top inset) arealso shown), as described in Example 5; 20 c a merge from uninjuredcontrol (no GFP (bright or light gray) fluorescence), 20 d and 20 e aremerges from the ischemic eyes 2 days 20 d and 7 days 20 e after systemichemangioblast administration (GFP+ cells appear as bright or lightgray). (20 f, ×600, confocal), fluorescent immunocytochemistrycolocalizes hemangioblast (hES-BC) cell-derived endothelial cells toexisting injured vasculature in cross sections of mouse eyes thatunderwent I/R injury; a high magnification view of a vascular lumen inthe ganglion cell layer adjacent to the inner limiting membrane showsthe lumen surrounded by endothelial cells (arrowhead, CD31) and also bymature endothelial cell(s) derived from hemangioblast (hES-BC) cells(arrow, human nuclear antigen). Inset upper and middle panels are theseparate human nuclear antigen and CD31 channels that were used to makethe composite image. Lower panel is a lower magnification of the sameregion, with the box showing the area depicted in all panels.V=vitreous; IPL=inner plexiform layer; RPE=retinal pigment epithelialcell layer; Ch=choroid. See Example 5.

FIGS. 21a-21f show the incorporation of hemangioblasts, or blast cellsor hES-BC cells, into the retinal vasculature of diabetic rats. 21 a and21 b show merged retinal vasculature images from diabetic rats 2 daysafter intravitreal hemangioblast administration, showing extensivehemangioblast incorporation (bright or light gray areas) into both largeand small vessels; 21 c, a merge from a control (non-diabetic) rat 2days after hemangioblast administration, showing that hemangioblasts (orhemangioblast-derived cells) did not incorporate into vasculature andformed a sheet that lay on top of the retina (light gray layer). (21 d,×100), a section from a non-diabetic control rat 2 days afterintravitreal blast cell injection, which is negative for human nuclearantigen staining, but is clearly positive for endothelium (CD31,arrows). (21 e, ×100) and (21 f, ×600, confocal) are rat eye sectionsfrom diabetic rats 2 days after intravitreal hemangioblast injection,and stained with CD31 and human nuclear antigen antibodies, whichclearly show colocalized staining with CD31 and human nuclear antigen incells lining vessel lumens in the ganglion cell layer of the retina,immediately posterior to the internal limiting membrane that separatesthe neural retinal from the vitreous (arrows pointing to bright areas).See Example 6.

FIGS. 22a-22i show endothelial differentiation in ischemic hind limbmuscle and infarcted heart after injection of hemangioblasts. 22 a, 22b, 22 h and 22 i: Differentiation of hemangioblasts or hES-BC cells ininfarcted hearts. (22 a (200×)), infarcted myocardium section fromcontrol mouse immunostained with human specific vWF antibody, showing nostain of human vWF; (22 b, 200×) and (22 i, ×600 confocal), infractedmyocardium section 4 weeks after injection of hemangioblasts,immunostained with human specific vWF antibody (light gray or brightareas in 22 b and 22 i); 22 h the survival curves of mice treated withsham operation, medium control, and hemangioblasts. 22 c-22 g:Differentiation of hemangioblasts in ishemic hind limb muscles. 22 c,50×), a hind limb muscle section from control mouse immunostained withhuman specific vWF antibody, showing no stain of human vWF; (22 d, 50×)and (22 e, 600×, confocal), ischemic hind limb muscle sections 4 weeksafter injection of hemangioblasts, immunostained with human specific vWFantibody (light gray); 22 f restoration of blood flow to surgicallyinduced ischemic limbs. Hind limb blood flow monitored serially for 3-30days after ligation in mouse receiving 6×10⁵ hemangioblasts and in mousewith medium only. Blood flow is calculated as the ratio of flow in theischemic limb to that in the non-ischemic limb; 22 g, laser Dopplerblood flow images. Images of controls (medium) and ischemic animalsinjected with BC cells (n=6 for each group). See Examples 7 and 8.

FIG. 23 shows immunostaining of GFP (the lightest or brightest areas)and cTnI (medium gray) on heart tissue sections from myocardialinfarcted (MI) mice (magnification 200×). See Example 8. The arrowsindicate double positive staining cells derived from injectedhemangioblast (hES-BC) cells.

FIGS. 24A-24B illustrate differentiation of hemangioblast (hES-BC) cellsinto smooth muscle cells. 24A Hemangioblasts express smooth musclespecific genes as determined by PCR of RNA isolated from hemangioblasts(hES-BCs). 24B The hemangioblasts (hES-BCs) also differentiate intosmooth muscle cells in vitro. Immunostaining for calponin and α-SMAshows that differentiated cells express these two smooth muscle cellmarkers.

DETAILED DESCRIPTION OF THE INVENTION

In order that the invention herein described may be fully understood,the following detailed description is set forth.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as those commonly understood by one of ordinaryskill in the art to which this invention belongs. Although methods andmaterials similar or equivalent to those described herein can be used inthe invention or testing of the present invention, suitable methods andmaterials are described below. The materials, methods and examples areillustrative only, and are not intended to be limiting.

All publications, patents, patent publications and applications andother documents mentioned herein are incorporated by reference in theirentirety.

Throughout this specification, the word “comprise” or variations such as“comprises” or “comprising” will be understood to imply the inclusion ofa stated integer or groups of integers but not the exclusion of anyother integer or group of integers.

In order to further define the invention, the following terms anddefinitions are provided herein.

The term “human embryonic stem cells” (hES cells) is used herein as itis used in the art. This term includes cells derived from the inner cellmass of human blastocysts or morulae that may be serially passaged ascell lines. The hES cells may be derived from fertilization of an eggcell with sperm or DNA, nuclear transfer, parthenogenesis, or by meansto generate hES cells with homozygosity in the HLA region. Human EScells are also cells derived from a zygote, blastomeres, orblastocyst-staged mammalian embryo produced by the fusion of a sperm andegg cell, nuclear transfer, parthenogenesis, or the reprogramming ofchromatin and subsequent incorporation of the reprogrammed chromatininto a plasma membrane to produce a cell. Human embryonic stem cells ofthe present invention may include, but are not limited to, ACT-4, No. 3,H1, H7, H9, H14 and ACT30 embryonic stem cells.

The term “protein transduction domain” (“PTD”) refers to any amino acidsequence that translocates across a cell membrane into cells or confersor increases the rate of, for example, another molecule (such as, forexample, a protein domain) to which the PTD is attached, to translocateacross a cell membrane into cells. The protein transduction domain maybe a domain or sequence that occurs naturally as part of a largerprotein (e.g., a PTD of a viral protein such as HIV TAT) or may be asynthetic or artificial amino acid sequence.

Overview

This invention provides a method for generating and expanding humanhemangio-colony forming cells from human embryo-derived cells,preparations and compositions comprising human hemangio-colony formingcells, methods of producing various cell types partially or terminallydifferentiated from hemangio-colony forming cells, methods of usinghemangio-colony forming cells therapeutically, and methods oftherapeutically using various cell types partially or terminallydifferentiated from hemangio-colony forming cells.

The terms “hemangioblast” and “hemangio-colony forming cells” will beused interchangeably throughout this application. These cells can bedescribed based on numerous structural and functional propertiesincluding, but not limited to, expression (RNA or protein) or lack ofexpression (RNA or protein) of one or more markers. Hemangio-colonyforming cells are capable of differentiating to give rise to at leasthematopoietic cell types or endothelial cell types. Hemangio-colonyforming cells are preferably bi-potential and capable of differentiatingto give rise to at least hematopoietic cell types and endothelial celltypes. As such, hemangio-colony forming cells of the present inventionare at least uni-potential, and preferably bi-potential. Additionallyhowever, hemangio-colony forming cells may have a greater degree ofdevelopmental potential and can, in certain embodiments, differentiateto give rise to cell types of other lineages. In certain embodiments,the hemangio-colony forming cells are capable of differentiating to giverise to other mesodermal derivatives such as cardiac cells (for example,cardiomyocytes) and/or smooth muscle cells.

This invention also provides a method for expanding mammalianhemangio-colony forming cells obtained from any source, including EScells, blastocysts or blastomeres, cord blood from placenta or umbilicaltissue, peripheral blood, bone marrow, or other tissue or by any othermeans known in the art. Human hemangio-colony forming cells can also begenerated from human embryo-derived cells. Human embryo-derived cellsmay be a substantially homogeneous population of cells, a heterogeneouspopulations of cells, or all or a portion of an embryonic tissue. As anexample of embryo-derived cells that can be used in the methods of thepresent invention, human hemangio-colony forming cells can be generatedfrom human embryonic stem cells. Such embryonic stem cells includeembryonic stem cells derived from or using, for example, blastocysts,plated ICMs, one or more blastomeres, or other portions of apre-implantation-stage embryo or embryo-like structure, regardless ofwhether produced by fertilization, somatic cell nuclear transfer (SCNT),parthenogenesis, androgenesis, or other sexual or asexual means.

In certain embodiments, hemangioblasts can be further differentiated tohematopoietic cells including, but not limited to, platelets and redblood cells. Such cells may be used in transfusions. The ability togenerate large numbers of cells for transfusion will alleviate thechronic shortage of blood experienced in blood banks and hospitalsacross the country. In certain embodiments, the methods of the inventionallow for the production of universal cells for transfusion.Specifically, red blood cells that are type O and Rh− can be readilygenerated and will serve as a universal blood source for transfusion.

The methods of this invention allow for the in vitro expansion ofhemangioblasts to large quantities useful for a variety of commercialand clinical applications. Expansion of hemangioblasts in vitro refersto the proliferation of hemangioblasts. While the methods of theinvention enable the expansion of human hemangioblast cells to reachcommercially useful quantities, the present invention also relates tolarge numbers of hemangioblast cells and to cell preparations comprisinglarge numbers of human hemangioblast cells (for example, at least10,000, 100,000, or 500,000 cells). In certain embodiments, the cellpreparations comprise at least 1×10⁶ cells. In other embodiments, thecell preparations comprise at least 2×10⁶ human hemangioblast cells andin further embodiments at least 3×10⁶ human hemangioblast cells. Instill other embodiments, the cell preparations comprise at least 4×10⁶human hemangioblast cells.

The present invention relates to a solution, a preparation, and acomposition comprising between 10,000 to 4 million or more mammalian(such as human) hemangioblast cells. The number of hemangioblast cellsin such a solution, a preparation, and a composition may be any numberbetween the range of 10,000 to 4 million, or more. This number could be,for example, 20,000, 50,000, 100,000, 500,000, 1 million, etc.

Similarly, the invention relates to preparations of human hemangioblastprogeny cells (e.g., human hematopoietic cells including humanhematopoietic stem cells, and endothelial cells). The invention furtherrelates to methods of producing, storing, and distributing hemangioblastcells and/or hemangioblast lineage cells.

The invention also provides methods and solutions suitable fortransfusion into human or animal patients. In particular embodiments,the invention provides methods of making red blood cells and/orplatelets, and/or other hematopoietic cell types for transfusion. Incertain embodiments, the invention is suitable for use in blood banksand hospitals to provide blood for transfusion following trauma, or inthe treatment of a blood-related disease or disorder. In certainembodiments, the invention provides red blood cells that are universaldonor cells. In certain embodiments, the red blood cells are functionaland express hemoglobin F prior to transfusion.

The invention also provides for human hemangio-colony forming cells,cell cultures comprising a substantially purified population of humanhemangio-colony forming cells, pharmaceutical preparations comprisinghuman hemangio-colony forming cells and cryopreserved preparations ofthe hemangio-colony forming cells. In certain embodiments, the inventionprovides for the use of the human hemangio-colony forming cells in themanufacture of a medicament to treat a condition in a patient in needthereof. Alternatively, the invention provides the use of the cellcultures in the manufacture of a medicament to treat a condition in apatient in need thereof. The invention also provides the use of thepharmaceutical preparations in the manufacture of a medicament to treata condition in a patient in need thereof.

The hemangio-colony forming cells can be identified and characterizedbased on their structural properties. Specifically, and in certainembodiments, these cells are unique in that they are only looselyadherent to each other (loosely adherent to other hemangio-colonyforming cells). Because these cells are only loosely adherent to eachother, cultures or colonies of hemangio-colony forming cells can bedissociated to single cells using only mechanical dissociationtechniques and without the need for enzymatic dissociation techniques.The cells are sufficiently loosely adherent to each other thatmechanical dissociation alone, rather than enzymatic dissociation or acombination of mechanical and enzymatic dissociation, is sufficient todisaggregate the cultures or colonies without substantially impairingthe viability of the cells. In other words, mechanical dissociation doesnot require so much force as to cause substantial cell injury or deathwhen compared to that observed subsequent to enzymatic dissociation ofcell aggregates.

Furthermore, hemangio-colony forming cells can be identified orcharacterized based on the expression or lack of expression (as assessedat the level of the gene or the level of the protein) of one or moremarkers. For example, in certain embodiments, hemangio-colony formingcells can be identified or characterized based on lack of expression ofone or more (e.g., the cells can be characterized based on lack ofexpression of at least one, at least two, at least three or at leastfour of the following markers) of the following cell surface markers:CD34, KDR, CD133, or CD31. Additionally or alternatively,hemangio-colony forming cells can be identified or characterized basedon expression of GATA2 and/or LMO2. Additionally or alternatively,hemangio-colony forming cells can be identified or characterized basedon expression or lack of expression (as assessed at the level of thegene or the level of the protein) of one or more markers analyzed inTable 2.

Hemangio-colony forming cells of the present invention can be identifiedor characterized based on one or any combination of these structural orfunctional characteristics. Note that although these cells can bederived from any of a number of sources, for example, embryonic tissue,prenatal tissue, or perinatal tissue, the term “hemangio-colony formingcells” applies to cells, regardless of source, that are capable ofdifferentiating to give rise to at least hematopoietic cell types and/orendothelial cell types and that have one or more of the foregoingstructural or functional properties.

In Vitro Differentiation of Human Embryonic Stem Cells to ObtainEmbryoid Bodies and Hemangioblasts

The present invention provides a method for generating and expandinghuman hemangioblasts derived from human embryonic stem cells, or fromhuman blastocysts or blastomeres. The hemangioblasts so produced may bepurified and/or isolated.

Human hemangio-colony forming cells can also be generated from humanembryo-derived cells. Human embryo-derived cells may be a substantiallyhomogeneous population of cells, a heterogeneous populations of cells,or all or a portion of an embryonic tissue. As an example ofembryo-derived cells that can be used in the methods of the presentinvention, human hemangio-colony forming cells can be generated fromhuman embryonic stem cells. Such embryonic stem cells include embryonicstem cells derived from or using, for example, blastocysts, plated ICMs,one or more blastomeres, or other portions of a pre-implantation-stageembryo or embryo-like structure, regardless of whether produced byfertilization, somatic cell nuclear transfer (SCNT), parthenogenesis,androgenesis, or other sexual or asexual means.

Additionally or alternatively, hemangio-colony forming cells can begenerated from other embryo-derived cells. For example, hemangio-colonyforming cells can be generated (without necessarily going through a stepof embryonic stem cell derivation) from or using plated embryos, ICMs,blastocysts, trophoblast/trophectoderm cells, one or more blastomeres,trophoblast stem cells, embryonic germ cells, or other portions of apre-implantation-stage embryo or embryo-like structure, regardless ofwhether produced by fertilization, somatic cell nuclear transfer (SCNT),parthenogenesis, androgenesis, or other sexual or asexual means.Similarly, hemangio-colony forming cells can be generated using cells orcell lines partially differentiated from embryo-derived cells. Forexample, if a human embryonic stem cell line is used to produce cellsthat are more developmentally primitive than hemangio-colony formingcells, in terms of development potential and plasticity, suchembryo-derived cells could then be used to generate hemangio-colonyforming cells.

Additionally or alternatively, hemangio-colony forming cells can begenerated from other pre-natal or peri-natal sources including, withoutlimitation, umbilical cord, umbilical cord blood, amniotic fluid,amniotic stem cells, and placenta.

It is noted that when hemangio-colony forming cells are generated fromhuman embryonic tissue a step of embryoid body formation may be needed.However, given that embryoid body formation serves, at least in part, tohelp recapitulate the three dimensional interaction of the germ layersthat occurs during early development, such a step is not necessarilyrequired when the embryo-derived cells already have a structure ororganization that serves substantially the same purpose as embryoid bodyformation. By way of example, when hemangio-colony forming cells aregenerated from plated blastocysts, a level of three dimensionalorganization already exists amongst the cells in the blastocyst. Assuch, a step of embryoid body formation is not necessarily required toprovide intercellular signals, inductive cues, or three dimensionalarchitecture.

The methods and uses of the present invention can be used to generatehemangio-colony forming cells from embryo-derived cells. In certainembodiments, the embryo-derived cells are embryonic stem cells. Incertain other embodiments, the embryo-derived cells are plated embryos,ICMs, blastocysts, trophoblast/trophectoderm cells, one or moreblastomeres, trophoblast stem cells, or other portions of an earlypre-implantation embryo. For any of the foregoing, the embryo-derivedcells may be from embryos produced by fertilization, somatic cellnuclear transfer (SCNT), parthenogenesis, androgenesis, or other sexualor asexual means.

Throughout this application, when a method is described by referringspecifically to generating hemangio-colony forming cells from embryonicstem cells, the invention similarly contemplates generatinghemangio-colony forming cells from or using other embryonic-derivedcells, and using the generated cells for any of the same therapeuticapplications.

In certain aspects of the invention, the human embryonic stem cells maybe the starting material of this method. The embryonic stem cells may becultured in any way known in the art, such as in the presence or absenceof feeder cells.

Embryonic stem cells may form embryoid bodies (“EBs”) in suspension inmedium containing serum (Wang et al. 2005 J Exp Med (201):1603-1614;Wang et al. 2004 Immunity (21): 31-41; Chadwick et al. 2003 Blood (102):906-915). The addition of serum, however, presents certain challenges,including variability in experiments, cost, the potential for infectiousagents, and limited supply. Further, for clinical and certain commercialapplications, use of serum necessitates additional U.S. andinternational regulatory compliance issues that govern biologicalproducts.

The present invention provides methods of generating and expanding humanhemangioblasts from embryonic stem cells in which no serum is used. Theserum-free conditions are more conducive to scale-up production undergood manufacturing process (GMP) guidelines than are conditions whichrequire serum. Furthermore, serum-free conditions extend the half-lifeof certain factors added to the medium (for example, the half-life ofproteins including growth factors, cytokines, and HOXB4 in media isincreased when no serum is present). In certain embodiments, serum-freemedia is used throughout the method of this invention for generating andexpanding human hemangioblasts.

In the first step of this method for generating and expanding humanhemangioblast cells, human stem cells are grown in serum-free media andare induced to differentiate into embryoid bodies. To induce embryoidbody formation, embryonic stem cells may be pelleted and resuspended inserum-free medium (e.g., in Stemline I or II media (Sigmam™))supplemented with one or more morphogenic factors and cytokines and thenplated on low attachment (e.g., ultra-low attachment) culture dishes.Morphogenic factors and cytokines may include, but are not limited to,bone morphogenic proteins (e.g., BMP2, BMP-4, BMP-7, but not BMP-3) andVEGF, SCF and FL. Bone morphogenic proteins and VEGF may be used aloneor in combination with other factors. The morphogenic factors andcytokines may be added to the media from 0-48 hours of cell culture.Following incubation under these conditions, incubation in the presenceof early hematopoietic expansion cytokines, including, but not limitedto, thrombopoietin (TPO), Flt-3 ligand, and stem cell factor (SCF),allows the plated ES cells to form EBs. In addition to TPO, Flt-3ligand, and SCF, VEGF, BMP-4, and HoxB4 may also be added to the media.In one embodiment, human ES cells are first grown in the presence ofBMP-4 and VEGF₁₆₅ (e.g., 25-100 ng/ml), followed by growing in thepresence of BMP-4, VEGF₁₆₅, SCF, TPO, and FLT3 ligand (e.g., 10-50ng/ml) and HoxB4 (e.g., 1.5-5 μg/ml of a triple protein transductiondomain-HoxB4 fusion protein as disclosed herein). The additional factorsmay be added 48-72 hours after plating.

In this method of the present invention, human hemangioblast cells areisolated from early embryoid bodies (“EBs”). Isolating hemangioblastcells from early EBs supports the expansion of the cells in vitro. Forhuman cells, hemangioblast cells may be obtained from EBs grown for lessthan 10 days. In certain embodiments of the present invention,hemangioblast cells arise in human EBs grown for 2-6 days. According toone embodiment, hemangioblast cells are identified and may be isolatedfrom human EBs grown for 4-6 days. In other embodiments, human EBs aregrown for 2-5 days before hemangioblast cells are isolated. In certainembodiments, human EBs are grown for 3-4.5 days before hemangioblastcells are isolated.

In certain embodiments, early EBs are washed and dissociated (e.g., byTrypsin/EDTA or collagenase B). A select number of cells (e.g., 2-5×10⁵cells) are then mixed with serum-free methylcellulose medium optimizedfor hemangioblast cell growth (e.g., BL-CFU medium, for example StemCell Technologies Catalogue H4436, or hemangioblast cell expansionmedium (HGM), or any medium containing 1.0% methylcellulose in MDM, 1-2%Bovine serum albumin, 0.1 mM 2-mercaptoethanol, 10 μg/ml rh-Insulin, 200μg/ml iron saturated human transferrin, 20 ng/ml rh-GM-CSF, 20 ng/mlrh-IL-3, 20 ng/ml rh-IL-6, 20 ng/ml rh-G-CSF) (“rh” stands for“recombinant human”). This medium may be supplemented with early stagecytokines (including, but not limited to, EPO, TPO, SCF, FL, FLt-3,VEGF, BMPs such as BMP2, BMP4 and BMP7, but not BMP3) and HOXB4 (oranother homeobox protein). In certain embodiments, erythropoietin (EPO)is added to the media. In further embodiments, EPO, SCF, VEGF, BMP-4 andHoxB4 are added to the media. In additional embodiments, the cells aregrown in the presence of EPO, TPO and FL. In certain embodiments whereH9 is the starting human ES cell line, EPO, TPO and FL are added to themedia. In addition to EPO, TPO and FL, media for cells derived from H9or other ES cells may further comprise VEGF, BMP-4, and HoxB4.

The cells so obtained by this method (the cells may be in BL-CFUmedium), which include hemangioblast cells, are plated onto ultra-lowattachment culture dishes and incubated in a CO₂ incubator to growhemangioblast colonies. Some cells may be able to form secondary EBs.Following approximately 3-6 days, and in some instances 3-4.5 days,hemangioblast colonies are observed. Hemangioblast colonies may bedistinguished from other cells such as secondary EBs by theirdistinctive grape-like morphology and/or by their small size. Inaddition, hemangioblasts may be identified by the expression of certainmarkers (e.g., the expression of both early hematopoietic andendothelial cell markers) as well as their ability to differentiate intoat least both hematopoietic and endothelial cells (see below, Derivinghemangioblast lineage cells). For example, while hemangioblasts lackcertain features characteristic of mature endothelial or hematopoieticcells, these cells may be identified by the presence of certain markers(such as, for example, CD71+) and the absence of other markers (forexample, CD34−). Hemangioblasts may also express GATA-1 and GATA-2proteins, CXCR-4, and TPO and EPO receptors. In addition, hemangioblastsmay be characterized by the absence or low expression of other markers(e.g., CD31, CD34, KDR, or other adhesion molecules). Further,hemangioblasts may be characterized by the expression of certain genes,e.g., genes associated with hemangioblasts and early primitiveerythroblast development, such as, for example, SCL, LMO2, FLT-1,embryonic fetal globin genes, NF-E2, GATA-1, EKLF, ICAM-4,glycophoriuns, and EPO receptor).

Accordingly, hemangioblasts may be isolated by size (being smaller thanthe other cells) or purified with an anti-CD71+ antibody, such as byimmunoaffinity column chromatography.

The hemangioblast cells may be isolated by size and/or morphology by thefollowing procedure. After 6 to 7 days of growth, the cell mixturecontains EBs, which are round and represent a clump of multiple cells,and hemangioblasts, which are grape-like, smaller than the EBs, and aresingle cells. Accordingly, hemangioblasts may be isolated based on theirmorphology and size. The hemangioblast cells may be manually picked, forexample, when observing the cell mixture under a microscope. The cellsmay subsequently grow into colonies, each colony having between 100-150cells.

Human hemangioblast colonies derived as described above may be pickedand replated onto methylcellulose CFU-medium to form hematopoietic CFUs.In certain embodiments, CFU-medium comprises StemCell TechnologiesH4436. In further embodiments, hemangioblasts are plated in Stemline IImedia supplemented with cytokines and other factors. For example,individual BL-CFC colonies may be handpicked and transferred to afibronectin-coated plate containing Stemline II with recombinant humanSCF (e.g, 20 ng/ml), TPO (e.g., 20 ng/ml), FL (e.g., 20 ng/ml), IL-3(e.g., 20 ng/ml) VEGF (e.g., 20 ng/ml), G-CSF (e.g., 20 n ng/ml), BMP-4(e.g., 15 ng/ml), IL-6 (e.g., 10 ng/ml), IGF-1 (e.g, 10 ng/ml),endothelial cell growth supplement (ECGS, e.g., 100 μg/ml), Epo (e.g., 3U/ml). Following one week of growth in vitro, non-adherent hematopoieticcells may be removed by gentle pipetting and used directly forhematopoietic CFU assay. Following removal of the non-adherent cells,the adherent populations may be grown for one more week in EGM-2endothelial cell medium (Cambrex™), and then examined for the expressionof vWF.

Expansion of Hemangioblasts In Vitro

Certain aspects of the invention relate to the in vitro expansion ofhemangioblasts. In certain embodiments, hemangioblasts expanded by themethods of the invention are obtained from early embryoid bodies derivedfrom human embryonic stem cells as described above.

In addition to deriving hemangioblasts from human embryonic stem cells(hES cells), hemangioblasts to be expanded may also be isolated fromother mammalian sources, such as mammalian embryos (Ogawa et al. 2001Int Rev Immunol (20):21-44, US patent publication no. 2004/0052771),cord blood from placenta and umbilical tissues (Pelosi, et al. 2002Blood (100): 3203-3208; Cogle et al. 2004 Blood (103):133-5), peripheralblood and bone marrow (Pelosi et al. 2002 Hematopoiesis (100):3203-3208). In certain embodiments, non-human hemangioblasts to beexpanded may be generated from non-human (such as mouse and non-humanprimates) embryonic stem cells. In certain embodiments, hemangioblastsare obtained from umbilical cord blood (UCB) or bone marrow by methodssuch as, for example, magnetic bead positive selection or purificationtechniques (e.g. MACS column). Cells may be selected based on theirCD71+ status and may be confirmed as CD34−. Further, the isolatedhemangioblasts may be tested for their potential to give rise to bothhematopoietic and endothelial cell lineages. In certain embodiments,hemangioblasts isolated or purified and optionally enriched fromembryos, cord blood, peripheral blood, bone marrow, or other tissue, aremore than 95% pure.

Bone marrow-derived cells may be obtained from any stage of developmentof the donor individual, including prenatal (e.g., embryonic or fetal),infant (e.g., from birth to approximately three years of age in humans),child (e.g., from about three years of age to about 13 years of age inhumans), adolescent (e.g., from about 13 years of age to about 18 yearsof age in humans), young adult (e.g., from about 18 years of age toabout 35 years of age in humans), adult (from about 35 years of age toabout 55 years of age in humans) or elderly (e.g. from about 55 yearsand beyond of age in humans).

Human bone marrow may be harvested by scraping from the split sternum ofa patient undergoing surgery, for example. Bone marrow may then bepreserved in tissue clumps of 0.1 to 1 mm³ in volume and then grown on amouse embryonic feeder layer (e.g., a mitomycin C-treated or irradiatedfeeder layer). The bone marrow cells will attach to the plates and overa period of 1-2 weeks of culture, hemangioblast cells may be identifiedbased on morphological features and/or cell markers and isolated (see USpatent publication no. 2004/0052771). The cells may then be subsequentlygrown and expanded in serum-free conditions according to the methodsdisclosed herein.

In addition, bone marrow cells and cells from blood or other tissue maybe fractionated to obtain hemangioblasts cells. Methods of fractionationare well known in the art, and generally involve both positive selection(i.e., retention of cells based on a particular property) and negativeselection (i.e., elimination of cells based on a particular property).Methods for fractionation and enrichment of bone marrow-derived cellsare best characterized for human and mouse cells.

There are a variety of methods known in the art for fractionating andenriching bone marrow-derived or other cells. Positive selection methodssuch as enriching for cells expressing CD71 may be used. And negativeselection methods which remove or reduce cells expressing CD3, CD10,CD11b, CD14, CD16, CD15, CD16, CD19, CD20, CD32, CD45, CD45R/B220 orLy6G may also be used alone or in combination with positive selectiontechniques. In the case of bone marrow cells, when the donor bonemarrow-derived cells are not autologous, negative selection may beperformed on the cell preparation to reduce or eliminate differentiatedT cells.

Generally, methods used for selection/enrichment of bone marrow-derived,blood, or other cells will utilize immunoaffinity technology, althoughdensity centrifugation methods are also useful. Immunoaffinitytechnology may take a variety of forms, as is well known in the art, butgenerally utilizes an antibody or antibody derivative in combinationwith some type of segregation technology. The segregation technologygenerally results in physical segregation of cells bound by the antibodyand cells not bound by the antibody, although in some instances thesegregation technology which kills the cells bound by the antibody maybe used for negative selection.

Any suitable immunoaffinity technology may be utilized forselection/enrichment of hemangioblasts from bone marrow-derived, blood,or other cells, including fluorescence-activated cell sorting (FACS),panning, immunomagnetic separation, immunoaffinity chromatography,antibody-mediated complement fixation, immunotoxin, density gradientsegregation, and the like. After processing in the immunoaffinityprocess, the desired cells (the cells bound by the immunoaffinityreagent in the case of positive selection, and cells not bound by theimmunoaffinity reagent in the case of negative selection) are collectedand may be subjected to further rounds of immunoaffinityselection/enrichment.

Immunoaffinity selection/enrichment is typically carried out byincubating a preparation of cells comprising bone marrow-derived cellswith an antibody or antibody-derived affinity reagent (e.g., an antibodyspecific for a given surface marker), then utilizing the bound affinityreagent to select either for or against the cells to which the antibodyis bound. The selection process generally involves a physicalseparation, such as can be accomplished by directing droplets containingsingle cells into different containers depending on the presence orabsence of bound affinity reagent (FACS), by utilizing an antibody bound(directly or indirectly) to a solid phase substrate (panning,immunoaffinity chromatography), or by utilizing a magnetic field tocollect the cells which are bound to magnetic particles via the affinityreagent (immunomagnetic separation). Alternatively, undesirable cellsmay be eliminated from the bone marrow-derived cell preparation using anaffinity reagent which directs a cytotoxic insult to the cells bound bythe affinity reagent. The cytotoxic insult may be activated by theaffinity reagent (e.g., complement fixation), or may be localized to thetarget cells by the affinity reagent (e.g., immunotoxin, such as ricin Bchain).

Although the methods described above refer to enrichment of cells from apreparation of bone marrow-derived or blood cells, one skilled in theart will recognize that similar positive and negative selectiontechniques may be applied to cell preparations from other tissues.

Certain aspects of the invention relate to the in vitro expansion ofhemangioblasts. In certain embodiments, hemangioblasts expanded by themethods of the invention are obtained from early embryoid bodies derivedfrom human embryonic stem cells as described above. In otherembodiments, the hemangioblasts are isolated or enriched from humantissue (e.g., placenta or cord blood, peripheral blood, bone marrow,etc.)

In certain embodiments, the hemangioblasts are expanded in the presenceof a homeodomain protein (also referred to herein as a homeoboxprotein). In further embodiments, the hemangioblasts are expanded in thepresence of HOXB4. In certain embodiments, HOXB4 is added to thehemangioblast cells throughout the method for expanding hemangioblastcells.

HOXB4 is a homeodomain transcription factor (also called HOX2F, HOX2,HOX-2.6, and in the rat HOXA5) that is expressed in vivo in the stemcell fraction of the bone marrow and that is subsequently down-regulatedduring differentiation. Expression of the HOXB4 gene is associated withthe maintenance of primitive stem cell phenotypes (Sauvageau et al. 1995Genes Dev 9: 1753-1765; Buske et al. 2002 Blood 100: 862-868;Thorsteinsdottir et al. 1999 Blood 94: 2605-2612; Antonchuk et al. 2001Exp Hematol 29: 1125-1134).

HOXB4 used in the methods of the present invention to generate andexpand hemangioblasts, includes, but is not limited to, full lengthHOXB4 (e.g., HOXB4 polypeptides specified by public accession numbersGI:13273315, GI:29351568, as well as any functional variants and activefragments thereof. The wildtype HOXB4 protein may be encoded by theamino acid sequence of SEQ ID NO: 1, SEQ ID NO: 3 or any otheralternative allelic forms of such protein. Such sequences may beaccessed via publicly available databases, such as Genbank. Further,HOXB4 may be ectopically expressed within the cell or may be provided inthe media. HOXB4 expressed ectopically may be operably linked to aninducible promoter. HOXB4 provided in the media may be excreted byanother cell type (e.g, a feeder layer) or added directly to the media.

The present invention also relates to fusion proteins comprising HOXB4(including fusion proteins comprising full length HOXB4, or HOXB4functional variants or active fragments of HOXB4). In addition to HOXB4,this fusion protein may also comprise any additional proteins, proteindomains or peptides. In certain embodiments, HOXB4 may be joined to aprotein transduction domain (PTD) to allow translocation of the proteinfrom the medium into the cells and subsequently into nuclearcompartments. Fusion proteins may or may not comprise one or more linkersequences located in between the protein domains.

Functional variants of HOXB4 include mutants of HOXB4 and alleleicvariants, and active fragments thereof. Functional variants of HOXB4include any HOXB4 polypeptides and active fragments thereof, that arecapable of expanding hemangioblasts according to the methods of thepresent invention. HOXB4 functional variants also include HOXB4polypeptides that exhibit greater transcriptional activity compared tothe native HOXB4 protein. HOXB4 variants include proteins with one ormore amino acid substitution, addition, and/or deletion in relation to awildtype HOXB4. HOXB4 variants also include, but are not limited to,polypeptides that are at least 75% similar to the sequence provided inSEQ ID NO: 1 or SEQ ID NO:3. Accordingly, HOXB4 variants includepolypeptides that are 80%, 85%, 90%, 95%, and 99% similar to the aminoacid sequence provided in SEQ ID NO: 1 or SEQ ID NO:3.

HOXB4 variants also include polypeptides encoded by nucleic acidsequences that are at least 80% identical to a nucleic acid sequenceencoding its complement (e.g., the wildtype HOXB4 protein may be encodedby nucleic acid sequences of SEQ ID NO: 2 (GI:85376187) or SEQ ID NO: 4(GI:29351567)). Thus, HOXB4 variants include HOXB4 polypeptides that areencoded by nucleic acid sequences that are 85%, 90%, 95%, and 99%identical to the sequence provided in SEQ ID NO: 2 or SEQ ID NO: 4 orcomplement thereto.

Nucleic acid sequences encoding HOXB4 also include, but are not limitedto, any nucleic acid sequence that hybridizes under stringent conditionsto a nucleic acid sequence of SEQ ID NO: 2 or 4, complement thereto, orfragment thereof. Similarly, nucleic acids which differ from the nucleicacids as set forth in SEQ ID NO: 2 or 4 due to degeneracy in the geneticcode are also within the scope of the invention. HOXB4 variantpolypeptides also include splice variants or other naturally occurringHOXB4 proteins or nucleic acid sequences.

Active fragments of HOXB4 include, but are not limited to, any fragmentof full length HOXB4 polypeptide that is capable of maintaininghemangioblasts according to the methods of the present invention.Accordingly, in one embodiment, a HOXB4 protein of the present inventionis a HOXB4 protein that lacks part of the N-terminus, such as, forexample, the N-terminal 31, 32, or 33 amino acids of full length HOXB4.

Any of the HOXB4 proteins may be fused with additional proteins orprotein domains. For example, HOXB4 may be joined to a proteintransduction domain (PTD).

Protein transduction domains, covalently or non-covalently linked toHOXB4, allow the translocation of HOXB4 across the cell membranes so theprotein may ultimately reach the nuclear compartments of the cells.

PTDs that may be fused with a HOXB4 protein include the PTD of the HIVtransactivating protein (TAT) (Tat 47-57) (Schwarze and Dowdy 2000Trends Pharmacol. Sci. 21: 45-48; Krosl et al. 2003 Nature Medicine (9):1428-1432). For the HIV TAT protein, the amino acid sequence conferringmembrane translocation activity corresponds to residues 47-57(YGRKKRRQRRR, SEQ ID NO: 5) (Ho et al., 2001, Cancer Research 61:473-477; Vives et al., 1997, J. Biol. Chem. 272: 16010-16017). Thissequence alone can confer protein translocation activity. The TAT PTDmay also be the nine amino acids peptide sequence RKKRRQRRR (SEQ ID NO:6) (Park et al. Mol Cells 2002 (30):202-8). The TAT PTD sequences may beany of the peptide sequences disclosed in Ho et al., 2001, CancerResearch 61: 473-477 (the disclosure of which is hereby incorporated byreference herein), including YARKARRQARR (SEQ ID NO: 7), YARAAARQARA(SEQ ID NO: 8), YARAARRAARR (SEQ ID NO: 9) and RARAARRAARA (SEQ ID NO:10).

Other proteins that contain PTDs that may be fused to HOXB4 proteins ofthe present invention include the herpes simplex virus 1 (HSV-1)DNA-binding protein VP22 and the Drosophila Antennapedia (Antp) homeotictranscription factor (Schwarze et al. 2000 Trends Cell Biol. (10):290-295). For Antp, amino acids 43-58 (RQIKIWFQNRRMKWKK, SEQ ID NO: 11)represent the protein transduction domain, and for HSV VP22 the PTD isrepresented by the residues DAATATRGRSAASRPTERPRAPARSASRPRRPVE (SEQ IDNO: 12). Alternatively, HeptaARG (RRRRRRR, SEQ ID NO: 13) or artificialpeptides that confer transduction activity may be used as a PTD of thepresent invention.

In additional embodiments, the PTD may be a PTD peptide that isduplicated or multimerized. In certain embodiments, the PTD is one ormore of the TAT PTD peptide YARAAARQARA (SEQ ID NO: 14). In certainembodiments, the PTD is a multimer consisting of three of the TAT PTDpeptide YARAAARQARA (SEQ ID NO: 15). A HOXB4 protein that is fused orlinked to a multimeric PTD, such as, for example, a triplicatedsynthetic protein transduction domain (tPTD), may exhibit reducedlability and increased stability in cells. Such a HOXB4 construct mayalso be stable in serum-free medium and in the presence of hES cells.

Techniques for making fusion genes encoding fusion proteins are wellknown in the art. Essentially, the joining of various DNA fragmentscoding for different polypeptide sequences is performed in accordancewith conventional techniques. In another embodiment, the fusion gene canbe synthesized by conventional techniques including automated DNAsynthesizers. Alternatively, PCR amplification of gene fragments can becarried out using anchor primers which give rise to complementaryoverhangs between two consecutive gene fragments which can subsequentlybe annealed to generate a chimeric gene sequence (see, for example,Current Protocols in Molecular Biology, eds. Ausubel et al., John Wiley& Sons: 1992).

In certain embodiments, a fusion gene coding for a purification leadersequence, such as a poly-(His) sequence, may be linked to the N-terminusof the desired portion of the HOXB4 polypeptide or HOXB4-fusion protein,allowing the fusion protein be purified by affinity chromatography usinga Ni²⁺metal resin. The purification leader sequence can then besubsequently removed by treatment with enterokinase to provide thepurified HOXB4 polypeptide (e.g., see Hochuli et al., (1987) J.Chromatography 411:177; and Janknecht et al., PNAS USA 88:8972).

In certain embodiments, a HOXB4 protein or functional variant or activedomain of it, is linked to the C-terminus or the N-terminus of a secondprotein or protein domain (e.g., a PTD) with or without an interveninglinker sequence. The exact length and sequence of the linker and itsorientation relative to the linked sequences may vary. The linker maycomprise, for example, 2, 10, 20, 30, or more amino acids and may beselected based on desired properties such as solubility, length, stericseparation, etc. In particular embodiments, the linker may comprise afunctional sequence useful for the purification, detection, ormodification, for example, of the fusion protein. In certainembodiments, the linker comprises a polypeptide of two or more glycines.

The protein domains and/or the linker by which the domains are fused maybe modified to alter the effectiveness, stability and/or functionalcharacteristics of HOXB4.

In certain embodiments, HOXB4 is ectopically expressed within thehemangioblast cell or is provided in the media. HOXB4 expressedectopically may be operably linked to a regulatory sequence. Regulatorysequences are art-recognized and are selected to direct expression ofthe HOXB4 polypeptide.

HOXB4 provided in the media may be excreted by another cell type. Theother cell type may be a feeder layer, such as a mouse stromal celllayer transduced to express excretable HOXB4. For example, HOXB4 may befused to or engineered to comprise a signal peptide, or a hydrophobicsequence that facilitates export and secretion of the protein.Alternatively, HOXB4, such as a fusion protein covalently ornon-covalently linked to a PTD, may be added directly to the media.Additionally, HOXB4 may be borne on a viral vector, such as a retroviralvector or an adenoviral vector. Such a vector could transduce either thehemangioblasts or other cells in their culture.

Depending on the HOXB4 protein used, in particular embodiments HOXB4 isadded to the media at selected times during the expansion of thehemangioblasts. Because the hemangioblasts are expanded in serum-freemedium, HOXB4 is relatively stable. Accordingly, in certain embodiments,a HOXB4 protein or fusion protein is added every day to the humanhemangioblasts. In other embodiments, a HOXB4 protein or fusion proteinis added every other day, and in still other embodiments, a HOXB4protein or fusion protein is added every 2 days. In one embodiment, aHOXB4 fusion protein, HOXB4-PTD, is added every 2 days to the media.

In certain embodiments, the hemangioblasts can be expanded in thepresence of any other growth factors or proteins that are present in anamount sufficient to expand such cells.

Hemangioblasts obtained from any source, including human or non-human EScells, bone marrow, placenta or umbilical cord blood, peripheral blood,or other tissue may be expanded according to the methods describedabove. Accordingly, in certain embodiments, a select number of purifiedhemangioblasts or enriched cells are mixed with serum-freemethylcellulose medium optimized for hemangioblast growth (e.g., BL-CFUmedium, see Example 1 and 2). This medium may be supplemented with earlystage cytokines (including, but not limited to, EPO, TPO, FL, VGF, BMPslike BMP2, BMP4 and BMP7, but not BMP3) and HOXB4. In certainembodiments, erythropoietin (EPO) is added to the media. In certainembodiments, EPO, TPO and FL are added to the media. The cells are thenplated onto ultra-low attachment culture dishes and grown in a CO₂incubator. As mentioned above, hemangioblast colonies exhibit adistinctive grape-like morphology and are comparatively smaller thanother cells and may consequently be distinguished from other cell types.The hemangioblasts may also be tested for markers as well as for theirability to differentiate further into either hematopoietic orendothelial cell lineages. The hemangioblasts are subsequently isolatedand expanded in vitro. Media that may be used for expansion includesserum-free methylcellulose medium optimized for hemangioblasts growth(e.g., BL-CFU) supplemented with early stage cytokines and HOXB4. Earlystage cytokines include, but are not limited to, EPO, TPO, FL, VEGF,BMPs like BMP2, BMP4 and BMP7, but not BMP3. In certain embodiments,erythropoietin (EPO) is added to the medium. In further embodiments,EPO, TPO and FL are added to the medium.

Accordingly, a medium for expanding hemangioblasts may comprise VEGF,SCF, EPO, BMP-4, and HoxB4; in certain embodiments the medium mayfurther comprise TPO and FL. For example, single cells prepared from EBscultured for approximately 3.5 days, were collected and dissociated by0.05% trypsin-0.53 mM EDTA (Invitrogen) for 2-5 min, and a single cellsuspension was prepared by passing through 22 G needle 3-5 times. Cellswere collected by centrifugation at 1,000 rpm for 5 min. Cell pelletswere resuspended in 50-200 μl of Stemline I media. To expandhemangioblasts, single cell suspension derived from differentiation of 2to 5×105 hES cells were mixed with 2 ml hemangioblast expansion media(HGM) containing 1.0% methylcellulose in Isocve's MDM, 1-2% Bovine serumalbumin, 0.1 mM 2-mercaptoethanol, 10 μg/ml rh-Insulin, 200 μg/ml ironsaturated human transferrin, 20 ng/ml rh-GM-CSF, 20 ng/ml rh-IL-3, 20ng/ml rh-IL-6, 20 ng/ml rh-G-CSF, 3 to 6 units/ml rh-Epo, 50 ng/mlrh-SCF, 50 ng/ml rh-VEGF and 50 ng/ml rh-BMP-4, and 1.5 μg/ml oftPTD-HoxB4, with/without 50 ng/ml of Tpo and FL. The cell mixtures wereplated on ultra-low dishes and incubated at 37° C. in 5% CO2 for 4-6days.

In certain situations it may be desirable to obtain hemangioblasts froma patient or patient relative and expand said hemangioblasts in vitro.Such situations include, for example, a patient scheduled to beginchemotherapy or radiation therapy, or other situations wherein anautologous HSC transplantation (using the patient's own stem cells) maybe used. Thus, the present invention provides methods of treatingpatients in need of cell-based therapy (for example, patients in need ofhematopoietic reconstitution or treatment, or blood vessel growth ortreatment of vascular injuries including ischemia, see below) using theexpanded hemangioblasts or hemangioblast lineage cells of the invention,wherein the hemangioblasts are obtained from the bone marrow, blood, orother tissue of the patient or a patient relative. Accordingly, incertain embodiments, methods of treating a patient in need ofhemangioblasts (or hemangioblast lineage cells) may comprise a step ofisolating hemangioblasts from the patient or a patient relative.Hemangioblasts isolated from the patient or patient relative may beexpanded in vitro according to the methods of the present invention andsubsequently administered to the patient. Alternatively the expandedhemangioblasts may be grown further to give rise to hematopoietic cellsor endothelial cells before patient treatment.

It is also possible to obtain human ES cells from such a patient by anymethod known in the art, such as somatic cell nuclear transfer.Hemangioblasts of that patient may then be generated and expanded fromhis own ES cells using a method of this invention. Those hemangioblastsor lineage derivatives thereof may be administered to that patient or tohis relatives.

Using the methods of the present invention, human hemangioblasts areexpanded to reach commercially large quantities which can besubsequently used in various therapeutic and clinical applications.Furthermore, the hemangioblasts obtained by the methods disclosed hereinmay be differentiated further to give rise to either hematopoietic orendothelial cell lineages for use in clinical applications.

The hemangioblasts obtained from the method of this invention forgenerating and expanding human hemangioblasts from human ES cells havethe potential to differentiate into at least endothelial cells orhematopoietic cells (i.e., they are at least bi-potential). Otherhemangioblasts may be bi-potential as well. Yet other hemangioblasts maybe able to differentiate into cells other than hematopoietic andendothelial cells, i.e., they are multi- or pluri-potential).

Engineering MHC Genes in Human Embryonic Stem Cells to ObtainReduced-Complexity Hemangioblasts

The human embryonic stem cells used as the starting point for the methodof generating and expanding human hemangioblast cells of this inventionmay also be derived from a library of human embryonic stem cells, eachof which is hemizygous or homozygous for at least one MHC allele presentin a human population. In certain embodiments, each member of saidlibrary of stem cells is hemizygous or homozygous for a different set ofMHC alleles relative to the remaining members of the library. In certainembodiments, the library of stem cells is hemizygous or homozygous forall MHC alleles that are present in a human population. In the contextof this invention, stem cells that are homozygous for one or morehistocompatibility antigen genes include cells that are nullizygous forone or more (and in some embodiments, all) such genes. Nullizygous for agenetic locus means that the gene is null at that locus, i.e., bothalleles of that gene are deleted or inactivated. Stem cells that arenullizygous for all MHC genes may be produced by standard methods knownin the art, such as, for example, gene targeting and/or loss ofheterozygocity (LOH). See, for example, United States patentpublications US 20040091936, US 20030217374 and US 20030232430, and U.S.provisional application No. 60/729,173, the disclosures of all of whichare hereby incorporated by reference herein.

Accordingly, the present invention relates to methods of obtaininghemangioblasts, including a library of hemangioblasts, with reduced MHCcomplexity. Hemangioblasts and hemangioblast lineage cells with reducedMHC complexity will increase the supply of available cells fortherapeutic applications as it will eliminate the difficultiesassociated with patient matching. Such cells may be derived from stemcells that are engineered to be hemizygous or homozygous for genes ofthe MHC complex.

A human ES cell may comprise modifications to one of the alleles ofsister chromosomes in the cell's MHC complex. A variety of methods forgenerating gene modifications, such as gene targeting, may be used tomodify the genes in the MHC complex. Further, the modified alleles ofthe MHC complex in the cells may be subsequently engineered to behomozygous so that identical alleles are present on sister chromosomes.Methods such as loss of heterozygosity (LOH) may be utilized to engineercells to have homozygous alleles in the MHC complex. For example, one ormore genes in a set of MHC genes from a parental allele can be targetedto generate hemizygous cells. The other set of MHC genes can be removedby gene targeting or LOH to make a null line. This null line can be usedfurther as the embryonic cell line in which to drop arrays of the HLAgenes, or individual genes, to make a hemizygous or homozygous bank withan otherwise uniform genetic background.

In one aspect, a library of ES cell lines, wherein each member of thelibrary is homozygous for at least one HLA gene, is used to derivehemangioblasts according to the methods of the present invention. Inanother aspect, the invention provides a library of hemangioblasts(and/or hemangioblast lineage cells), wherein several lines of ES cellsare selected and differentiated into hemangioblasts. Thesehemangioblasts and/or hemangioblast lineage cells may be used for apatient in need of a cell-based therapy.

Accordingly, certain embodiments of this invention pertain to a methodof administering human hemangioblasts, hematopoietic stem cells, orhuman endothelial cells that have been derived from reduced-complexityembryonic stem cells to a patient in need thereof. In certainembodiments, this method comprises the steps of: (a) identifying apatient that needs treatment involving administering humanhemangioblasts, hematopoietic stem cells, or human endothelial cells tohim or her; (b) identifying MHC proteins expressed on the surface of thepatient's cells; (c) providing a library of human hemangioblasts ofreduced MHC complexity made by the method for generating and expandinghuman hemangioblast cells in vitro of the present invention; (d)selecting the human hemangioblast cells from the library that match thispatient's MHC proteins on his or her cells; (e) optionallydifferentiating the human hemangioblast cells identified in step (d)into human hematopoietic stem cells, endothelial cells or both, or cellsthat are further differentiated in either or both of these two lineages,depending on need; (f) administering any of the cells from step (d)and/or (e) to said patient. This method may be performed in a regionalcenter, such as, for example, a hospital, a clinic, a physician'soffice, and other health care facilities. Further, the hemangioblastsselected as a match for the patient, if stored in small cell numbers,may be expanded prior to patient treatment.

Human Hemangio-Colony Forming Cells/Hemangioblasts

In certain aspects, the present invention provides human hemangio-colonyforming cells. These cells are a unique, primitive cell type with avariety of therapeutic and other uses. Furthermore, this cell typeprovides an important tool for studying development of at least thehematopoietic and/or endothelial lineages. As such, the inventioncontemplates various preparations (including pharmaceuticalpreparations) and compositions comprising human hemangio-colony formingcells, as well as preparations (including pharmaceutical preparations)and compositions comprising one or more cell types partially orterminally differentiated from hemangio-colony forming cells.

The terms “hemangioblast” and “hemangio-colony forming cells” will beused interchangeably throughout this application. These cells can bedescribed based on numerous structural and functional propertiesincluding, but not limited to, expression (RNA or protein) or lack ofexpression (RNA or protein) of one or more markers. Hemangio-colonyforming cells are capable of differentiating to give rise to at leasthematopoietic cell types or endothelial cell types. Hemangio-colonyforming cells are preferably bi-potential and capable of differentiatingto give rise to at least hematopoietic cell types and endothelial celltypes. As such, hemangio-colony forming cells of the present inventionare at least uni-potential, and preferably bi-potential. Additionallyhowever, hemangio-colony forming cells may have a greater degree ofdevelopmental potential and can, in certain embodiments, differentiateto give rise to cell types of other lineages. In certain embodiments,the hemangio-colony forming cells are capable of differentiating to giverise to other mesodermal derivatives such as cardiac cells (for example,cardiomyocytes) and/or smooth muscle cells.

Furthermore, hemangio-colony forming cells can be identified andcharacterized based on their structural properties. Specifically, and incertain embodiments, these cells are unique in that they are onlyloosely adherent to each other (loosely adherent to otherhemangio-colony forming cells). Because these cells are only looselyadherent to each other, cultures or colonies of hemangio-colony formingcells can be dissociated to single cells using only mechanicaldissociation techniques and without the need for enzymatic dissociationtechniques. The cells are sufficiently loosely adherent to each otherthat mechanical dissociation alone, rather than enzymatic dissociationor a combination of mechanical and enzymatic dissociation, is sufficientto disaggregate the cultures or colonies without substantially impairingthe viability of the cells. In other words, mechanical dissociation doesnot require so much force as to cause substantial cell injury or deathwhen compared to that observed subsequent to enzymatic dissociation ofcell aggregates.

Furthermore, hemangio-colony forming cells can be identified orcharacterized based on the expression or lack of expression (as assessedat the level of the gene or the level of the protein) of one or moremarkers. For example, in certain embodiments, hemangio-colony formingcells can be identified or characterized based on lack of expression ofone or more (e.g., the cells can be characterized based on lack ofexpression of at least one, at least two, at least three or at leastfour of the following markers) of the following cell surface markers:CD34, KDR, CD133, or CD31. Additionally or alternatively,hemangio-colony forming cells can be identified or characterized basedon expression of GATA2 and/or LMO2. Additionally or alternatively,hemangio-colony forming cells can be identified or characterized basedon expression or lack of expression (as assessed at the level of thegene or the level of the protein) of one or more markers analyzed inTable 2.

Hemangio-colony forming cells of the present invention can be identifiedor characterized based on one or any combination of these structural orfunctional characteristics. Note that although these cells can bederived from any of a number of sources, for example, embryonic tissue,prenatal tissue, or perinatal tissue, the term “hemangio-colony formingcells” applies to cells, regardless of source, that are capable ofdifferentiating to give rise to at least hematopoietic cell types and/orendothelial cell types and that have one or more of the foregoingstructural or functional properties.

To illustrate, human hemangio-colony forming cells of the presentinvention have at least one of the following structural characteristics:(a) can differentiate to give rise to at least hematopoietic cell typesor endothelial cell types; (b) can differentiate to give rise to atleast hematopoietic cell types and endothelial cell types; (c) areloosely adherent to each other (to other human hemangio-colony formingcells; (d) do not express CD34 protein; (e) do not express CD31 protein;(f) do not express KDR protein; (g) do not express CD133 protein; (h)express GATA2 protein; (i) express LMO2 protein. In certain embodiments,human hemangio-colony forming cells have at least two, at least three,at least four, at least five, at least six, at least seven, at leasteight, or at least nine of the structural or functional characteristicsdetailed herein.

The invention provides for human hemangio-colony forming cells. Suchcells can differentiate to produce at least hematopoietic and/orendothelial cell types. In certain embodiments, the cells arecharacterized as being loosely adherent to other human hemangio-colonyforming cells. Alternatively or additionally, these cells may also bedescribed based on expression or lack of expression of certain markers.For example, these cells may also be described based on lack ofexpression of at least one of the following proteins: CD34, KDR, CD133,and CD31.

As detailed above, one of the interesting properties of humanhemangio-colony forming cells is that they are loosely adherent to eachother. Because these cells are only loosely adherent to each other,cultures or colonies of hemangio-colony forming cells can be dissociatedto single cells using only mechanical dissociation techniques andwithout the need for enzymatic dissociation techniques. The cells aresufficiently loosely adherent to each other that mechanical dissociationalone, rather than enzymatic dissociation or a combination thereof, issufficient to disaggregate the cultures or colonies withoutsubstantially impairing the viability of the cells. In other words,mechanical dissociation does not require so much force as to causesubstantial cell injury or death.

This property is not only useful in describing the cells anddistinguishing them phenotypically from other cell types, but it alsohas significant therapeutic implications. For example, relatively largenumbers (greater than 1×10⁶ or even greater than 1×10⁷ or even greaterthan 1×10⁸) of the hemangio-colony forming cells can be injected intohumans or other animals with substantially less risk of causing clots oremboli, or otherwise lodging in the lung. This is a significant advancein cellular therapy. The ability to safely administer relatively largenumbers of cells makes cellular therapy practical and possible for theeffective treatment of an increasing number of diseases and conditions.

The term “loosely adherent” is described qualitatively above and refersto behavior of the human hemangio-colony forming cells with respect toeach other. Cultures or colonies of hemangio-colony forming cells can bedissociated to single cells using only mechanical dissociationtechniques and without the need for enzymatic dissociation techniques.The cells are sufficiently loosely adherent to each other thatmechanical dissociation alone, rather than enzymatic dissociation or acombination thereof, is sufficient to disaggregate the cultures orcolonies without substantially impairing the viability of the cells. Inother words, mechanical dissociation does not require so much force asto cause substantial cell injury or death.

The term can also be described more quantitatively. For example and incertain embodiments, the term “loosely adherent” is used to refer tocultures or colonies of hemangio-colony forming cells wherein at least50% of the cells in the culture can be dissociated to single cells usingonly mechanical dissociation techniques and without the need forenzymatic dissociation techniques. In other embodiments, the term refersto cultures in which at least 60%, 65%, 70%, or 75% of the cells in theculture can be dissociated to single cells using only mechanicaldissociation techniques and without the need for enzymatic dissociationtechniques. In still other embodiments, the term refers to cultures inwhich at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or even 100% ofthe cells in the culture can be dissociated to single cells using onlymechanical dissociation techniques and without the need for enzymaticdissociation techniques.

The ability to dissociate the hemangio-colony forming cells using onlymechanical dissociation techniques and without the need for enzymaticdissociation techniques can be further quantitated based on the healthand viability of the cells following mechanical dissociation. In otherwords, if dissociation without enzymatic techniques requires so muchmechanical force that a significant number of the cells are damaged orkilled, the cells are not loosely adherent, as defined herein. Forexample and in certain embodiments, the term “loosely adherent” refersto cultures of cells that can be dissociated to single cells using onlymechanical dissociation techniques and without the need for enzymaticdissociation techniques, without substantially impairing the health orviability or the cells in comparison to that observed when the samecells are dissociated using enzymatic dissociation techniques. Forexample, the health or viability of the cells is decreased by less than15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or even less than 1% incomparison to that observed when a culture of the same cells aredissociated using enzymatic dissociation techniques.

Exemplary enzymatic dissociation techniques include, but are not limitedto, treatment with trypsin, collagenase, or other enzymes that disruptcell-cell or cell-matrix interactions. Exemplary mechanical dissociationtechniques include, but are not limited to, one or more passages througha pipette.

Human hemangio-colony forming cells according to the present inventionare defined structurally and functionally. Such cells can be generatedfrom any of a number of sources including from embryonic tissue,prenatal tissue, perinatal tissue, and even from adult tissue. By way ofexample, human hemangio-colony forming cells can be generated from humanembryonic stem cells, other embryo-derived cells (blastocysts,blastomeres, ICMs, embryos, trophoblasts/trophectoderm cells,trophoblast stem cells, primordial germ cells, embryonic germ cells,etc.), amniotic fluid, amniotic stem cells, placenta, placental stemcells, and umbilical cord.

The invention provides human hemangio-colony forming cells, compositionscomprising human hemangio-colony forming cells, and preparations(including pharmaceutical preparations) comprising human hemangio-colonyforming cells. Certain features of these aspects of the invention aredescribed in detail below. The invention contemplates combinations ofany of the following aspects and embodiments of the invention.

In one aspect, the invention provides a human hemangio-colony formingcell. The cell can differentiate to produce at least hematopoieticand/or endothelial cell types. In certain embodiments, the cell isloosely adherent to other human hemangio-colony forming cells. Incertain embodiments, the cell does not express CD34 protein. In certainother embodiments, the cell does not express one or more of (e.g., thecell does not express at least one, at least two, at least three, or atleast four of the following proteins) the following proteins: CD34,CD31, CD133, KDR. In certain other embodiments, the cell does expressGATA2 and/or LMO2 protein. In certain other embodiments, the cellexpresses or does not express one or more (e.g., at least one, two,three, four, five, six, seven, eight, nine, ten, etc.) of the markersprovided in Table 2. In certain other embodiments, the cell has anexpression profile as depicted in Table 2.

In another aspect, the invention provides a human hemangio-colonyforming cell. The cell, which cell can differentiate to produce at leasthematopoietic and/or endothelial cell types, and the cell does notexpress any of the following proteins: CD34, CD31, KDR, and CD133. Incertain embodiments, the cell is loosely adherent to other humanhemangio-colony forming cells. In other embodiments, the cell doesexpress GATA2 and/or LMO2 protein. In certain other embodiments, thecell expresses or does not express one or more (e.g., at least one, two,three, four, five, six, seven, eight, nine, ten, etc) of the markersprovided in Table 2. In certain other embodiments, the cell has anexpression profile as depicted in Table 2.

In another aspect, the invention provides a cell culture comprising asubstantially purified population of human hemangio-colony formingcells. The cells can differentiate to produce at least hematopoietic andendothelial cell types, and the cells are loosely adherent to eachother. In certain embodiments, the cell does not express CD34 protein.In certain other embodiments, the cell does not express one or more of(e.g., the cell does not express at least one, at least two, at leastthree, or at least four of the following proteins) the followingproteins: CD34, CD31, CD133, KDR. In certain other embodiments, the celldoes express GATA2 and/or LMO2 protein. In certain other embodiments,the cell expresses or does not express one or more (one, two, three,four, five, six, seven, eight, nine, ten, etc) of the markers providedin Table 2. In certain other embodiments, the cell has an expressionprofile as depicted in Table 2.

In another aspect, the invention provides a cell culture comprisinghuman hemangio-colony forming cells differentiated from embryonictissue. In certain embodiments, the hemangio-colony forming cells areloosely adherent to each other. In certain embodiments, the cells candifferentiate to produce at least hematopoietic and/or endothelial celltypes, and the cells are loosely adherent to each other. In certainembodiments, the cell does not express CD34 protein. In certain otherembodiments, the cell does not express one or more of (e.g., the celldoes not express at least one, at least two, at least three, or at leastfour of the following proteins) the following proteins: CD34, CD31,CD133, KDR. In certain other embodiments, the cell does express GATA2and/or LMO2 protein. In certain other embodiments, the cell expresses ordoes not express one or more (one, two, three, four, five, six, seven,eight, nine, ten, etc) of the markers provided in Table 2. In certainother embodiments, the cell has an expression profile as depicted inTable 2.

In another aspect, the invention provides a cell culture comprisinghuman hemangio-colony forming cells, which cells can differentiate toproduce at least hematopoietic and/or endothelial cell types. In certainembodiments, the cells are loosely adherent to each other. In certainembodiments, the cell does not express CD34 protein. In certain otherembodiments, the cell does not express one or more of (e.g., the celldoes not express at least one, at least two, at least three, or at leastfour of the following proteins) the following proteins: CD34, CD31,CD133, KDR. In certain other embodiments, the cell does express GATA2and/or LMO2 protein. In certain other embodiments, the cell expresses ordoes not express one or more (one, two, three, four, five, six, seven,eight, nine, ten, etc) of the markers provided in Table 2. In certainother embodiments, the cell has an expression profile as depicted inTable 2.

In another aspect, the invention provides a pharmaceutical preparationcomprising human hemangio-colony forming cells, which cells candifferentiate to produce at least hematopoietic and/or endothelial celltypes. In certain embodiments, the hemangio-colony forming cells areloosely adherent to each other. In certain embodiments, the cell doesnot express CD34 protein. In certain other embodiments, the cell doesnot express one or more of (e.g., the cell does not express at leastone, at least two, at least three, or at least four of the followingproteins) the following proteins: CD34, CD31, CD133, KDR. In certainother embodiments, the cell does express GATA2 and/or LMO2 protein. Incertain other embodiments, the cell expresses or does not express one ormore (one, two, three, four, five, six, seven, eight, nine, ten, etc) ofthe markers provided in Table 2. In certain other embodiments, the cellhas an expression profile as depicted in Table 2. The pharmaceuticalpreparation can be preparing using any pharmaceutically acceptablecarrier or excipient.

In another aspect, the invention provides a pharmaceutical preparationcomprising human hemangio-colony forming cells, wherein thehemangio-colony forming cells do not express any of the followingproteins: CD34, CD31, KDR, and CD133. In certain embodiments, thehemangio-colony forming cells can differentiate to produce at leasthematopoietic and/or endothelial cell types. In certain embodiments, thehemangio-colony forming cells are loosely adherent to each other. Incertain other embodiments, the cell does express GATA2 and/or LMO2protein. In certain other embodiments, the cell expresses or does notexpress one or more (one, two, three, four, five, six, seven, eight,nine, ten, etc) of the markers provided in Table 2. In certain otherembodiments, the cell has an expression profile as depicted in Table 2.The pharmaceutical preparation can be preparing using anypharmaceutically acceptable carrier or excipient.

In certain embodiments of any of the foregoing, the composition orpharmaceutical preparation comprises at least 1×10⁵ humanhemangio-colony forming cells. In certain other embodiment, of any ofthe foregoing, the composition or pharmaceutical preparation comprisesat least 1×10⁶, at least 5×10⁶, at least 1×10⁷, or greater than 1×10⁷human hemangio-colony forming cells.

Additional cells, compositions, and preparations include cells partiallyor terminally differentiated from human hemangio-colony forming cells.For example, the invention contemplates compositions and preparationscomprising one or more hematopoietic and/or endothelial cell typedifferentiated from a hemangio-colony forming cell. Exemplaryhematopoietic cell types include hematopoietic stem cells, platelets,RBCs, lymphocytes, megakaryocytes, and the like. By way of furtherexamples, the invention contemplates compositions and preparationscomprising one or more other cell type, such as one or more partially orterminally differentiated mesodermal cell type, differentiated fromhemangio-colony forming cells.

In certain embodiments of any of the foregoing, the invention provides acryopreserved preparation of human hemangio-colony cells or cellspartially or terminally differentiated therefrom.

In certain embodiments of any of the foregoing, the invention providesfor the therapeutic use of human hemangio-colony forming cells, orcompositions or preparations of human hemangio-colony forming cells.Such cells and preparations can be used in the treatment of any of theconditions or diseases detailed throughout the specification, as well asin the blood banking industry. Furthermore, cells differentiated fromhuman hemangio-colony forming cells, or compositions or preparations ofhuman hemangio-colony forming cells, can be used therapeutically in thetreatment of any of the conditions or diseases detailed throughout thespecification, as well as in the blood banking industry.

The human hemangio-colony forming cells of the invention are can be usedtherapeutically. Additionally or alternatively, human hemangio-colonyforming cells can be used to study development of endothelial andhematopoietic lineages or in screening assays to identify factors thatcan be used, for example, to (i) maintain human hemangio-colony formingcells or (ii) to promote differentiation of human hemangio-colonyforming cells to one or more partially or terminally differentiated celltypes. Furthermore, human hemangio-colony forming cells can be used togenerate one or more partially or terminally differentiated cell typesfor in vitro or in vivo use.

The human hemangio-colony forming cells of the invention can be used inany of the methods or application described in the present applicationincluding, but not limited to, in the treatment of any of the diseasesor conditions described herein.

Cell Preparations Comprising Hemangioblasts Expanded in Vitro

In certain embodiments of the present invention, mammalian (includinghuman) hemangioblasts are expanded to reach commercial quantities andare used in various therapeutic and clinical applications. In particularembodiments, hemangioblasts are expanded to reach cell numbers on theorder of 10,000 to 4 million (or more). These cell numbers may bereached within 3-4 days of starting the initial preparations.Accordingly, the present invention relates to preparations comprisinglarge numbers of hemangioblasts, said preparations comprising at least10,000, 50,000, 100,000, 500,000, a million, 2 million, 3 million or 4million cells.

This invention also provides for a solution, a composition, and apreparation comprising large numbers of hemangioblasts, said solution,said composition, and said preparation comprising at least 10,000,50,000, 100,000, 500,000, a million, 2 million, 3 million or 4 millioncells. The hemangioblasts could be human.

Other aspects of the present invention relate to differentiating thehemangioblasts obtained by the methods disclosed herein into eitherhematopoietic or endothelial cell lineages, or both, that aresubsequently used in clinical applications. Thus, the present inventionalso relates to cell preparations comprising large numbers ofhematopoietic or endothelial cells. The invention also relates todifferentiating the hemangioblasts obtained by the methods disclosedherein into other cell lineages, other than hematopoietic andendothelial cells. Thus, the present invention also relates to cellpreparations comprising large numbers of other hemangioblast-derivedcells.

Compositions and preparations comprising large numbers (e.g, thousandsor millions) of hemangioblasts may be obtained by expandinghemangioblasts that are obtained as described above. Accordingly, theinvention pertains to compositions and preparations comprising largenumbers of hemangioblasts achieved by expanding ES cells (such as humanES cells) or hemangioblasts obtained from cord blood, peripheral bloodor bone marrow. Further, as the methods of expansion may be applied tohemangioblasts of mouse, rat, bovine, or non-human primate origin, forexample, the present invention also relates to compositions andpreparations comprising large numbers of hemangioblasts of other speciesin addition to human. The hemangioblasts to be expanded by the methodsof this invention may be bi-potential, i.e., can differentiate intoeither endothelial cells or hematopoietic stem cells. In certainembodiments, the human hemangioblasts generated and expanded from humanES cells are bi-potential. Hemangio-colony forming cells are capable ofdifferentiating to give rise to at least hematopoietic cell types orendothelial cell types. Hemangio-colony forming cells are preferablybi-potential and capable of differentiating to give rise to at leasthematopoietic cell types and endothelial cell types. As such,hemangio-colony forming cells of the present invention are at leastuni-potential, and preferably bi-potential. Additionally however,hemangio-colony forming cells may have a greater degree of developmentalpotential and can, in certain embodiments, differentiate to give rise tocell types of other lineages. In certain embodiments, thehemangio-colony forming cells are capable of differentiating to giverise to other mesodermal derivatives such as cardiac cells (for example,cardiomyocytes) and/or smooth muscle cells.

Mammalian Hemangioblast Cell Markers

As described above, the hemangio-colony forming cells lack certainfeatures characteristic of mature endothelial or hematopoietic cells.These hemangio-colony forming cells or hemangioblasts, however, may beidentified by various markers such as, for example, CD71+, GATA-1 andGATA-2 proteins, CXCR-4, and TPO and EPO receptors. In additionalembodiments, the hemangioblasts express LMO-2. Hemangioblasts mayadditionally be characterized by the absence or low expression of othermarkers. Accordingly, hemangioblasts may be CD34- CD31-, and KDR-. Infurther embodiments, the hemangioblasts may be CD34-, CD31-, KDR-, andCD133-.

Accordingly, in certain embodiments, the hemangioblasts generated andexpanded by the methods of present invention are characterized by thepresence or absence of any one or more of the markers listed in Table 2.For example, the hemangioblasts may test negative for expression of anyone or more of the markers listed in Table 2 that is denoted as “−”under “BL-CFC”. Accordingly, in some embodiments, the hemangioblasts maybe negative for CD34 expression. The cells may additionally oralternatively be negative for CD31, CD133, and/or KDR expression. Infurther embodiments, the hemangioblasts may express any of the markersdenoted in Table 2 with “+”. For example, the cells may express one ormore of the markers LMO-2 and GATA-2. Expression of a marker may beassessed by any method, such as, for example, immunohistochemistry orimmunoblotting to test for protein expression, or mRNA analysis to testfor expression at the RNA level.

Deriving Hemangioblast Lineage Cells

The methods and cell preparations of the present invention also relateto hemangioblast derivative cells. Human hemangioblasts generated andexpanded by this invention and mammalian hemangioblasts expanded by themethods of the invention may be differentiated in vitro to obtainhematopoietic cells (including hematopoietic stem cells (HSCs)) orendothelial cells, as well as cells that are further differentiated inthese two lineages. These cells may subsequently be used in thetherapeutic and commercial applications described below.

In certain embodiments, hematopoietic cells are derived by growing thehemangioblasts in serum-free BL-CFU for 3-10 days. In other embodiments,single-cell suspensions of hES-derived BL-CFC cells are grown for 10-14days. Maintaining serum-free conditions is optimal insofar as serum-freeconditions facilitate scale-up production and compliance with regulatoryguidelines as well as reduce cost. Hemangioblasts of the presentinvention may also be grown in serum-free Hem-culture (Bhatia et al.1997 J Exp Med (186): 619-624), which sustains human hematopoietic stemcells and comprises BSA (e.g, 1% BSA), insulin (e.g., 5 μg/ml humaninsulin), transferrin media or transferrin (e.g., 100 μg/ml humantransferrin), L-glutamine, beta-mercaptoethanol (e.g., 10⁻⁴ M), andgrowth factors. The growth factors may comprise SCF (e.g., 300 ng/ml),granulocytic-colony-stimulating factor (G-CSF) (e.g., 50 ng/ml), Flt-3(e.g., 300 ng/ml), IL-3 (e.g., 10 ng/ml), and IL-6 (e.g., 10 ng/ml).Other factors useful for obtaining hematopoietic cells fromhemangioblasts include thrombopoietin (TPO) and VEGF (see, for example,Wang et al. 2005 Ann NY Acad Sci (1044): 29-40) and BMP-4. Thehemangioblasts may also be grown in serum-free methylcellulose mediumsupplemented with a multilineage hematopoietic growth factor cocktail.Thus, the hemangioblasts may be grown in methylcellulose in Iscovemodified Dulbecco medium (IMDM) comprising BSA, saturated humantransferrin, human LDL, supplemented with early acting growth factors(e.g, c-kit ligand, flt3 ligand), multilineage growth factors (e.g.,IL-3, granulocyte macrophage-CSF (GM-CSF)), and unilineage growthfactors (e.g., G-CSF, M-CSF, EPO, TPO)), VEGF, and bFGF. Alternatively,the hemangioblasts may be grown in medium comprising unilineage growthfactors to support the growth of one type of hematopoietic cell (e.g,red blood cells, macrophages, or granulocytes).

In one embodiment, hemangioblast colonies are resuspended in Stemline Imedia. Cells are then mixed with 1 ml of serum-free hematopoietic CFUmedia (H4436, Stem Cell Technologies™) plus 1.5 μg/ml of tPTD-HoxB4 and0.5% EX-CYTE (Serologicals Proteins Inc.™). The cell mixtures are thenplated on cell culture untreated plates and incubated at 37° C. for10-14 days. Hematopoietic CFUs arising following 10-14 days afterinitial plating may be characterized morphologically, such as bystaining with Wright-Giemsa dye.

Hematopoietic cells may also be derived from the hemangioblast usingother conditions known in the art (e.g., in media comprising IMDM, 30%fetal calf serum (FCS), 1% bovine serum albumin (BSA), 10⁻⁴ Mbeta-mercaptoethanol, and 2 mM L-glutamine). Further, in otherembodiments basic fibroblast growth factor may be used to promote bothBL-CFC frequency within EBs and promote hematopoietic differentiation(Faloon et al. 2000 Development (127): 1931-1941). In yet otherembodiments, the growth factor hemangiopoietin (HAPO) is used to promotegrowth and hematopoietic differentiation of the hemangioblasts (Liu etal. 2004 Blood (103): 4449-4456). The differentiation into hematopoieticcells may be assessed by CD45 status (CD45+) and the CFU assay, forexample.

To form hematopoietic cells, human hemangioblasts may be grown for 3-10days, or optionally for longer periods of time (e.g., 10-14 days) inCFU-medium. Human hemangioblasts of the present invention are able toform CFUs comprising granulocytes, erythrocytes, macrophages, andmegakaryocytes (CFU-GEMM/mix) as well as colony forming units containingonly one of the latter cell types (e.g., CFU-G, CFU-E, CFU-M, andCFU-GM). In certain embodiments, single-cell suspensions of hES-derivedBL-CFC cells are grown for 10-14 days to derive hematopoietic cells suchas, for example, erythroid, myeloid, macrophage, and multilineagehematopoietic cells.

Other aspects of the invention relate to endothelial cells derived fromthe human hemangioblasts obtained and expanded or mammalianhemangioblasts expanded by the methods described herein. Thehemangioblasts may be grown in conditions favorable to endothelialmaturation.

In certain embodiments of the present invention, to obtain endothelialcells, hemangioblasts are first plated onto a fibronectin-coated surfaceand following 3-5 days (or in other embodiments 3-7 days), are replatedonto a thick layer of Matrigel to support differentiation intoendothelial cells. These conditions maintain the serum-free conditionsestablished during hemangioblast development. Alternatively,hemangioblasts may be grown in media known to support differentiationinto endothelial cells. Such conditions include, for example,Endo-culture comprising 20% fetal bovine serum (FBS), 50 ng/mlendothelial cell growth supplement (i.e., pituitary extracts), 10 IU/mlheparin, and 5 ng/ml human VEGF-A₁₆₅ (Terramani et al. 2000 In VitroCell Dev Biol Anim (36): 125-132). Other conditions known in the artinclude medium supplemented with 25% FCS/horse serum, and in someembodiments heparin (e.g., 10 U/ml), insulin like growth factor (IGF1)(e.g, 2 ng), and EC growth supplement (ECGS, e.g., 100 μg). The growthfactors VEGF and EGF may also be used in combination with HAPO tosupport endothelial differentiation (Liu et al. 2004). Thehemangioblasts may also be seeded onto dishes coated with collagen andfibronectin, for example, to promote differentiation into endothelialcells. Cells may be analyzed for von Willebrand factor (vWF) andendothelial nitric oxide synthase (eNOS) and the ability to form anendothelial network in vitro.

Accordingly, to form endothelial cells, hemangioblast colonies derivedby the methods described above are picked and replated ontofibronectin-coated culture plates optimized for the first step towardsendothelial differentiation. The cells may be plated in EGM-2 or EGM-2MVcomplete media (Cambrexm). Following 3 to 5 days, and in alternativeembodiments 3 to 7 days, the cells are re-plated on a surface thatsupports endothelial differentiation, such as on a layer of Matrigel.Following 16-24 hours of incubation, the formation of branchedtube-cords (see FIG. 8, for example) suggests typical endothelial cellbehavior. Endothelial-specific assays such as LDL-uptake may also beused to confirm that these cells are of endothelial nature.

In other aspects of the invention, human hemangioblasts generated andexpanded by this invention and mammalian hemangioblasts expanded by themethods of the invention may be differentiated in vitro to obtain othercells, as well as cells that are further differentiated from these celllineages. Such additional cell lineages may be derived from thehemangioblasts generated and expanded by this invention and mammalianhemangioblasts expanded by the methods of the invention because thehemangioblast cells may have an even greater degree of developmentalpotential beyond differentiating into hematopoietic and endothelialcells.

Clinical and Commercial Embodiments of Human Hemangioblasts andHemangioblast Lineage Cells Cell-Based Therapies

While human hemangioblast cells have the potential to differentiate invivo into either hematopoietic or endothelial cells, they can be used incell-based treatments in which either of these two cell types are neededor would improve treatment. Further, a patient may be treated with anytherapy or treatment comprising hemangioblast lineage cells (i.e.,hematopoietic cells and/or endothelial cells). The following sectiondescribes methods of using the human hemangioblasts of this inventiongenerated and expanded by the methods of this invention, or expanded bythe methods of this invention.

In certain embodiments of the present invention, treatments to increaseor treat hematopoietic cells and treatments for increasing blood vesselgrowth and/or facilitating blood vessel repair are contemplated.Accordingly, in certain aspects, the present invention relates tomethods and compositions for treating a patient in need of hematopoieticcells or blood vessel growth or repair. The hemangioblasts may beinjected into the blood vessel of a subject or be administered to theblood vessel of a subject through operation. The patient or the subjectmay be human.

In certain embodiments of the present invention, human hemangioblastcells are used in transplantation, where HSC transplantation wouldotherwise be used. Such transplantation may be used, for example, inhematopoietic reconstitution for the treatment of patients with acute orchronic leukemia, aplastic anemia and various immunodeficiencysyndromes, as well as various non-hematological malignancies andauto-immune disorders, and to rescue patients from treatment-inducedaplasia following high-dose chemotherapy and/or radiotherapy. Suchtransplantation may be achieved in vivo or ex vivo (such as in bonemarrow transplant).

In other embodiments of the invention, human hemangioblast cells areused to treat patients in need of hematopoietic reconstitution orhematopoietic treatment. Such patients in include, for example, patientswith thalassemias, sickle cell anemia, aplastic anemia (also calledhypoplastic anemia), cytopenia, marrow hypoplasia, platelet deficiency,hematopoietic malignancies such as leukemias, paroxysmal nocturnalhemoglobinuria (PNH), and ADA (e.g., deaminase (ADA)-deficient severecombined immunodeficiency (SCID)).

Particular embodiments of the present invention therefore relate tomethods of treating a patient in need of hematopoietic reconstitution orhematopoietic treatment using the hemangioblasts of the invention.Accordingly, the invention relates to methods of treating a patient inneed of hematopoetic reconstitution or treatment comprising selecting apatient in need thereof, generating and expanding or expanding humanhemangioblasts according to the methods of the present invention, andadministering the human hemangioblasts into the patient. Alternatively,the method may comprise differentiating the generated and expanded orexpanded human hemangioblasts into human hematopoietic cells andsubsequently administering the hematopoietic cells to the patient.

Alternative embodiments include methods in which human hemangioblastsare produced on a large scale and stored prior to the selection of apatient in need thereof. Thus, other embodiments of the invention relateto methods of treating a patient in need of hematopoietic reconstitutionor treatment comprising selecting a patient in need thereof, placing anorder for human hemangioblasts already isolated and expanded accordingto the methods described above, and administering said humanhemangioblasts to the patient. Likewise, the method may comprisedifferentiating said human hemangioblasts into human hematopoietic cellsand administering said hematopoietic cells to the patient. In additionalembodiments, hemangioblasts hemizygous or homozygous for at least oneMHC allele are grown, optionally grown to commercial quantities, andoptionally stored by a business entity. When a patient presents a needfor such cells or hemangioblast lineage cells, a clinician or hospitalwill place an order with the business for such cells.

Because the human hemangioblast cells of the invention will proliferateand differentiate into endothelial cells under an angiogenicmicroenvironment, the human hemangioblast cells may be used in atherapeutic manner to provide new blood vessels or to induce repair ofdamaged blood vessels at a site of injury in a patient. Thus in certainaspects, the present invention relates to methods of promoting new bloodvessel growth or repairing injured vasculature. The human hemangioblastsof the present invention may be used to treat endothelial injury, suchas myocardium infarction, stroke and ischemic brain, ischemic limbs andskin wounds including ischemic limbs and wounds that occur in diabeticanimals or patients, and ischemic reperfusion injury in the retina.Other ischemic conditions that may be treated with the hemangioblasts ofthe present invention include renal ischemia, pulmonary ischemia, andischemic cardiomyopathy. Hemangioblasts may also be used to help repairinjured blood vessels following balloon angioplasty or deployment of anendovascular stent. Hemangioblasts may additionally be used in tissuegrafting, surgery and following radiation injury. Further, thehemangioblasts may be used to treat and/or prevent progression ofatherosclerosis as well as to repair endothelial cell damage that occursin systemic sclerosis and Raynaud's phenomenon (RP) (Blann et al. 1993 JRheumatol. (20):1325-30).

Accordingly, the invention provides various methods involved inproviding blood vessel growth or repair to a patient in need thereof. Inone embodiment, the invention provides for a method for inducingformation of new blood vessels in an ischemic tissue in a patient inneed thereof, comprising administering to said patient an effectiveamount of the purified preparation of human hemangioblast cellsdescribed above to induce new blood vessel formation in said ischemictissue. Thus certain aspects of the present invention provide a methodof enhancing blood vessel formation in a patient in need thereof,comprising selecting the patient in need thereof, isolating humanhemangioblast cells as described above, and administering thehemangioblast cells to the patient. In yet another aspect, the presentinvention provides a method for treating an injured blood vessel in apatient in need thereof, comprising selecting the patient in needthereof, expanding or generating and expanding human hemangioblast cellsas described above, and administering the hemangioblast cells to thepatient. In addition to the aforementioned embodiments, thehemangioblasts may be produced on a large scale and stored prior to theselection of patient in need of hemangioblasts. In further embodiments,hemangioblasts hemizygous or homozygous for at least one MHC allele aregrown, optionally grown to commercial quantities, and optionally storedbefore a patient is selected for hemangioblast treatment. Any of theaforementioned hemangioblasts or hemangioblast cell preparations may beadministered directly into the circulation (intravenously). In certainembodiments (e.g., where vascular repair is necessary in the eye, suchas in the treatment of ischemia/reperfusion injury to the retina), thehemangioblast cells or hemangioblast cell preparations may beadministered by intra-vitreous injection.

Administration of the solutions or preparations of hemangioblasts orderivative cells thereof may be accomplished by any route and may bedetermined on a case by case basis. Also, an effective amount to beadministered of these solutions or preparations of hemangioblasts orderivative cells thereof is an amount that is therapeutically effectiveand may be determined on a case by case basis.

In further aspects, hemangioblast lineage cells are used in therapeuticapplications, including in the treatment of the indications describedabove, for example. Accordingly, hemangioblasts generated and expandedor expanded by the methods described herein are differentiated in vitrofirst to obtain hematopoetic and/or endothelial cells, and then toobtain cells that are further differentiated in these two lineages.These cells may be subsequently administered to a subject or patient totreat hematopoetic conditions or for hematopoietic reconstitution, orfor the treatment of ischemia or vascular injury, for example.

HSCs derived from the human hemangioblasts obtained by the methodsdisclosed herein are grown further to expand the HSCs and/or to deriveother hematopoietic lineage cell types. Certain aspects of the presentinvention relate to the use of HSCs derived from the hemangioblasts intransplantation. In additional embodiments, differentiated hematopoieticcells (such as, for example, granulocytes, erythrocytes, myeloid cells,megakaryocytes, platelets, macrophages, mast cells and neutrophils(Wiles and Keller 1991 Development (111): 259)) are used in varioustreatments such as transfusion therapy or for the treatment ofinfections. Accordingly, other embodiments of the present inventionrelate to methods of treating a patient in need of hematopoeticreconstitution or treatment using the HSCs or hematopoetic lineage cellsderived from hemangioblasts of the invention.

In certain aspects, therefore, the present invention relates to methodsof treating a patient in need of hematopoetic cells or treatmentcomprising selecting a patient in need thereof, expanding or isolatingand expanding human hemangioblasts according to the methods of thepresent invention, differentiating said hemangioblast cells intohematopoetic stem cells and/or mature hematopoetic cells, andadministering the hematopoietic cells to the patient.

In other aspects of the invention, the hemangioblasts are grown to giverise to endothelial cells according to the methods disclosed herein. Theendothelial may subsequently be used to provide new blood vessels or toinduce repair of damaged blood vessels at a site of injury in a patient.Thus in certain aspects, the present invention relates to methods ofpromoting new blood vessel growth or repairing injured vasculature inwhich endothelial cells derived from hemangioblasts are used as atherapy. The endothelial cells may be used to treat endothelial injury,such as myocardium infarction and pulmonary ischemia, stroke andischemic brain, ischemic limbs and skin wounds including ischemic limbsand wounds that occur in diabetic animals or patients, ischemicreperfusion injury in the retina, renal ischemia. The endothelial cellsmay also be used to help repair injured blood vessels following balloonangioplasty or deployment of an endovascular stent as well as ingrafting, surgery and following radiation injury. Further, theendothelial cells may be used to treat and/or prevent progression ofatherosclerosis as well as to repair endothelial cell damage that occursin systemic sclerosis and Raynaud's phenomenon.

The endothelial cell may be further differentiated and those cells, asappropriate, may be used in treating one or more of the “endothelialcell” disease or conditions, such as those listed in the precedingparagraph.

Accordingly, certain aspects of the invention relate to methods oftreating a patient with endothelial or vascular injury or in need ofblood vessel growth or repair comprising selecting a patient in needthereof, expanding or isolating and expanding human hemangioblastsaccording to the methods of the present invention, differentiating saidhemangioblast cells into endothelial cells, and administering theendothelial cells to the patient.

Blood Banking

Another aspect of the present invention provides methods of producinghematopoietic cells suitable for transfusion. Although such cells andmethods have numerous uses, a particularly important use would be inimproving the availability of blood for transfusions. In certainpreferred embodiments, the invention provides red blood cellsdifferentiated from hemangioblasts/hemangio-colony forming units. Suchdifferentiated red blood cells could be used for transfusions.

Further aspects of the invention relate to methods of generatingdifferentiated hematopoietic cells from hemangioblasts/hemangio-colonyforming units for use in blood transfusions for those in need thereof.In certain embodiments, differentiated hematopoietic cells aretransfused to treat trauma, blood loss during surgery, blood diseasessuch as anemia, Sickle cell anemia, or hemolytic diseases, or malignantdisease. In certain embodiments, red blood cells are transfused to treattrauma, blood loss during surgery, or blood diseases such as anemia,Sickle cell anemia, or hemolytic disease. In certain embodiments,platelets are transfused to treat congenital platelet disorders ormalignant disease. In certain embodiments, a mixed population of redblood cells and platelets are transfused.

It should be noted that many differentiated hematopoietic cell types,particularly red blood cells, typically exist in vivo as a mixedpopulation. Specifically, circulating red blood cells of varying levelsof age and differentiation are found in vivo. Additionally, red bloodcells mature over time so as to express less fetal hemoglobulin and moreadult hemoglobin. The present invention contemplates transfusion ofeither purified populations of red blood cells or of a mixed populationof red blood cells having varying levels of age and levels ofdifferentiation. In particular embodiments, the invention contemplatestransfusion of red blood cells expressing fetal hemoglobin (hemoglobinF).

This invention provides a method for producing differentiatedhematopoietic cells from human hemangio-colony forming cells in vitro,said method comprising the steps of:

(a) providing human hemangio-colony forming cells; and

b) differentiating said hemangio-colony forming cells intodifferentiated hematopoietic cells.

This invention also provides a method for performing blood transfusionsusing hematopoietic cells that were differentiated in vitro from humanhemangio-colony forming cells, said method comprising the steps of:

(a) providing human hemangio-colony forming cells;

(b) differentiating said hemangio-colony forming cells intodifferentiated hematopoietic cells; and

(c) performing blood transfusions with said differentiated hematopoieticcells.

This invention also provides a method for performing blood transfusionsusing hematopoietic cells that had been differentiated in vitro fromhuman hemangio-colony forming cells, said method comprising the stepsof:

(a) culturing a cell culture comprising human embryonic stem cells inserum-free media in the presence of at least one growth factor in anamount sufficient to induce the differentiation of said embryonic stemcells into embryoid bodies;

(b) adding at least one growth factor to said culture comprisingembryoid bodies and continuing to culture said culture in serum-freemedia, wherein said growth factor is in an amount sufficient to expandhuman hemangio-colony forming cells in said embryoid bodies culture;

(c) differentiating said hemangio-colony forming cells intodifferentiated hematopoietic cells; and

(d) performing blood transfusions with said differentiated hematopoieticcells.

In certain embodiments, said stem cells, embryoid bodies andhemangio-colony forming are grown in serum-free media throughout steps(a) and (b) of said method.

This invention also provides a method for performing blood transfusionsusing hematopoietic cells that had been differentiated in vitro fromhuman hemangio-colony forming cells, said method comprising the stepsof:

(a) culturing a cell culture comprising human embryo-derived cells inserum-free media in the presence of at least one growth factor in anamount sufficient to induce the differentiation of said embryo-derivedcells into embryoid bodies;

(b) adding at least one growth factor to said culture comprisingembryoid bodies and continuing to culture said culture in serum-freemedia, wherein said growth factor is in an amount sufficient to expandhuman hemangio-colony forming cells in said embryoid bodies culture;

(c) disaggregating said embryoid bodies into single cells;

(d) adding at least one growth factor to said culture comprising saidsingle cells and continuing to culture said culture in serum-free media,wherein said growth factor is in an amount sufficient to expand humanhemangio-colony forming cells in said culture comprising said singlecells;

(e) differentiating said hemangio-colony forming cells intodifferentiated hematopoietic cells; and

(f) performing blood transfusions with said differentiated hematopoieticcells.

In certain embodiments, said embryo-derived cells, embryoid bodies,hemangio-colony forming cells and single cells are grown in serum-freemedia throughout steps (a)-(d) of said method.

In certain embodiments, the embryo-derived cell is an embryonic stemcell.

In certain embodiments, the growth factor is a protein that comprises ahomeobox protein, or a functional variant or an active fragment thereof.In certain embodiments, the homeobox protein comprises a HOXB4 protein,or a functional variant or an active fragment thereof.

In certain embodiments, the differentiated hematopoietic cells areproduced as a single cell type such as red blood cells, platelets, andphagocytes. Note, however, that when a single cell type is produced, thecell type may be heterogeneous in terms of the level of maturity ordifferentiation of the particular cell type. By way of example,differentiated red blood cells may be heterogeneous in terms of level ofmaturity and cellular age. Without being bound by theory, suchheterogeneity of erythrocytic cells may be beneficial because it mimicsthe way in which red blood cells are found in vivo.

In certain embodiments, the single cell types are mixed to equal theproportion of differentiated cell types that is found in blood. Incertain embodiments, multiple differentiated hematopoietic cell typesare produced in the same step. In certain embodiments, the phagocyte isselected from: granulocytes: neutrophils, basophils, eosinophils,lymphocytes or monocytes. In certain embodiments, the hematopoietic celltypes are produced in a proportion approximately equal to the proportionof differentiated hematopoietic cell types found in blood, 96% red bloodcells, 1% platelets, and 3% phagocytes. In certain embodiments, plasmais added to the differentiated hematopoietic cells before transfusion.In certain embodiments, packed cells, for example packed red bloodcells, are transfused in the absence or substantial absence of plasma.

In certain embodiments, the differentiated hematopoietic cells producedfrom the methods of the application are functional. In certainembodiments, the platelets produced from the methods of the applicationare functional. In certain embodiments, the phagocytes produced from themethods of the application are functional. In certain embodiments, thered blood cells produced from the methods of the application arefunctional. In certain embodiments, the red blood cells expresshemoglobin F prior to transfusion. In certain embodiments, the red bloodcells carry oxygen. In certain embodiments, the red blood cells have alifespan equal to naturally derived red blood cells. In certainembodiments, the red blood cells have a lifespan that is 75% of that ofnaturally derived red blood cells. In certain embodiments, the red bloodcells have a lifespan that is 50% of that of naturally derived red bloodcells. In certain embodiments, the red blood cells have a lifespan thatis 25% of that of naturally derived red blood cells.

In certain embodiments, the methods of the application produce 1×10⁶cells per 100 mm dish. In certain embodiments, 2×10⁶ cells are producedper 100 mm dish. In certain embodiments, 3×10⁶ cells are produced per100 mm dish. In certain embodiments, 4×10⁶ cells are produced per 100 mmdish. In certain embodiments, 5×10⁶ cells are produced per 100 mm dish.In certain embodiments, 6×10⁶ cells are produced per 100 mm dish. Incertain embodiments, 7×10⁶ cells are produced per 100 mm dish. Incertain embodiments, 8×10⁶ cells are produced per 100 mm dish. Incertain embodiments, 9×10⁶ cells are produced per 100 mm dish. Incertain embodiments, 1×10⁷ cells are produced per 100 mm dish. Incertain embodiments, 5×10⁷ cells are produced per 100 mm dish. Incertain embodiments, 1×10⁸ cells are produced per 100 mm dish.

In certain embodiments, the differentiation step is performed usingconditions known to one of skill in the art as discussed above. Incertain embodiments, the differentiation step is performed using methodsspecific to differentiate cells into red blood cells (see WO2005/118780,herein incorporated by reference). In certain embodiments, thedifferentiation step is performed using methods specific todifferentiate cells into platelets. In certain embodiments, thedifferentiation step is performed using methods specific todifferentiate cells into leukocytes.

Differentiation agents which can be used according to the presentinvention include cytokines such as interferon-alpha A, interferon-alphaA/D, interferon-.beta., interferon-gamma, interferon-gamma-inducibleprotein-10, interleukin-1, interleukin-2, interleukin-3, interleukin-4,interleukin-5, interleukin-6, interleukin-7, interleukin-8,interleukin-9, interleukin-10, interleukin-1, interleukin-12,interleukin-13, interleukin-15, interleukin-17, keratinocyte growthfactor, leptin, leukemia inhibitory factor, macrophagecolony-stimulating factor, and macrophage inflammatory protein-1 alpha.

Differentiation agents according to the invention also include growthfactors such as 6Ckine (recombinant), activin A, AlphaA-interferon,alpha-interferon, amphiregulin, angiogenin, B-endothelial cell growthfactor, beta cellulin, B-interferon, brain derived neurotrophic factor,C10 (recombinant), cardiotrophin-1, ciliary neurotrophic factor,cytokine-induced neutrophil chemoattractant-1, endothelial cell growthsupplement, eotaxin, epidermal growth factor, epithelial neutrophilactivating peptide-78, erythropoietin, estrogen receptor-alpha, estrogenreceptor-B, fibroblast growth factor (acidic/basic, heparin stabilized,recombinant), FLT-3/FLK-2 ligand (FLT-3 ligand), gamma-interferon, glialcell line-derived neurotrophic factor, Gly-His-Lys, granulocytecolony-stimulating factor, granulocyte macrophage colony-stimulatingfactor, GRO-alpha/MGSA, GRO-B, GRO-gamma, HCC-1, heparin-bindingepidermal growth factor like growth factor, hepatocyte growth factor,heregulin-alpha (EGF domain), insulin growth factor binding protein-1,insulin-like growth factor binding protein-1/IGF-1 complex, insulin-likegrowth factor, insulin-like growth factor II, 2.5S nerve growth factor(NGF), 7S-NGF, macrophage inflammatory protein-1B, macrophageinflammatory protein-2, macrophage inflammatory protein-3 alpha,macrophage inflammatory protein-3B, monocyte chemotactic protein-1,monocyte chemotactic protein-2, monocyte chemotactic protein-3,neurotrophin-3, neurotrophin-4, NGF-B (human or rat recombinant),oncostatin M (human or mouse recombinant), pituitary extract, placentagrowth factor, platelet-derived endothelial cell growth factor,platelet-derived growth factor, pleiotrophin, rantes, stem cell factor,stromal cell-derived factor 1B/pre-B cell growth stimulating factor,thrombopoetin, transforming growth factor alpha, transforming growthfactor-B1, transforming growth factor-B2, transforming growth factor-B3,transforming growth-factor-B5, tumor necrosis factor (alpha and B), andvascular endothelial growth factor.

Differentiation agents according to the invention also include hormonesand hormone antagonists, such as 17B-estradiol, adrenocorticotropichormone, adrenomedullin, alpha-melanocyte stimulating hormone, chorionicgonadotropin, corticosteroid-binding globulin, corticosterone,dexamethasone, estriol, follicle stimulating hormone, gastrin 1,glucagon, gonadotropin, hydrocortisone, insulin, insulin-like growthfactor binding protein, L-3,3′,5′-triiodothyronine,L-3,3′,5-triiodothyronine, leptin, leutinizing hormone, L-thyroxine,melatonin, MZ-4, oxytocin, parathyroid hormone, PEC-60, pituitary growthhormone, progesterone, prolactin, secretin, sex hormone bindingglobulin, thyroid stimulating hormone, thyrotropin releasing factor,thyroxine-binding globulin, and vasopressin.

In addition, differentiation agents according to the invention includeextracellular matrix components such as fibronectin, proteolyticfragments of fibronectin, laminin, thrombospondin, aggrecan, andsyndezan.

Differentiation agents according to the invention also includeantibodies to various factors, such as anti-low density lipoproteinreceptor antibody, anti-progesterone receptor, internal antibody,anti-alpha interferon receptor chain 2 antibody, anti-c-c chemokinereceptor 1 antibody, anti-CD 118 antibody, anti-CD 119 antibody,anti-colony stimulating factor-1 antibody, anti-CSF-1 receptor/c-finsantibody, anti-epidermal growth factor (AB-3) antibody, anti-epidermalgrowth factor receptor antibody, anti-epidermal growth factor receptor,phospho-specific antibody, anti-epidermal growth factor (AB-1) antibody,anti-erythropoietin receptor antibody, anti-estrogen receptor antibody,anti-estrogen receptor, C-terminal antibody, anti-estrogen receptor-Bantibody, anti-fibroblast growth factor receptor antibody,anti-fibroblast growth factor, basic antibody, anti-gamma-interferonreceptor chain antibody, anti-gamma-interferon human recombinantantibody, anti-GFR alpha-1 C-terminal antibody, anti-GFR alpha-2C-terminal antibody, anti-granulocyte colony-stimulating factor (AB-1)antibody, anti-granulocyte colony-stimulating factor receptor antibody,anti-insulin receptor antibody, anti-insulin-like growth factor-1receptor antibody, anti-interleukin-6 human recombinant antibody,anti-interleukin-1 human recombinant antibody, anti-interleukin-2 humanrecombinant antibody, anti-leptin mouse recombinant antibody, anti-nervegrowth factor receptor antibody, anti-p60, chicken antibody,anti-parathyroid hormone-like protein antibody, anti-platelet-derivedgrowth factor receptor antibody, anti-platelet-derived growth factorreceptor-B antibody, anti-platelet-derived growth factor-alpha antibody,anti-progesterone receptor antibody, anti-retinoic acid receptor-alphaantibody, anti-thyroid hormone nuclear receptor antibody, anti-thyroidhormone nuclear receptor-alpha 1/Bi antibody, anti-transferrinreceptor/CD71 antibody, anti-transforming growth factor-alpha antibody,anti-transforming growth factor-B3 antibody, anti-tumor necrosisfactor-alpha antibody, and anti-vascular endothelial growth factorantibody.

This invention also provides a library of differentiated hematopoieticcells that can provide matched cells to potential patient recipients asdescribed above. In certain embodiments, the cells are stored frozen.Accordingly, in one embodiment, the invention provides a method ofconducting a pharmaceutical business, comprising the step of providingdifferentiated hematopoietic cell preparations that are homozygous forat least one histocompatibility antigen, wherein cells are chosen from abank of such cells comprising a library of human hemangio-colony formingcells that can be expanded by the methods disclosed herein, wherein eachhemangio-colony forming cell preparation is hemizygous or homozygous forat least one MHC allele present in the human population, and whereinsaid bank of hemangio-colony forming cells comprises cells that are eachhemizygous or homozygous for a different set of MHC alleles relative tothe other members in the bank of cells. As mentioned above, genetargeting or loss of heterozygosity may be used to generate thehemizygous or homozygous MHC allele stem cells used to derive thehemangio-colony forming cells. In certain embodiments, hemangio-colonyforming cells of all blood types are included in the bank. In certainembodiments, hemangio-colony forming cells are matched to a patient toensure that differentiated hematopoietic cells of the patient's ownblood type are produced. In certain embodiments, hemangio-colony formingcells are negative for antigenic factors A, B, Rh, or any combinationthereof. In certain embodiments, the differentiated hematopoietic cellsare universal donor cells. By way of example, hematopoietic cells thatare type O and Rh negative can be universally used for bloodtransfusion. In certain embodiments, the invention provides methods forproducing type O, Rh negative red blood cells for universal transfusion.

In certain embodiments, red blood cells differentiated fromhemangio-colony forming cells express fetal hemoglobin. Transfusion ofred blood cells that express fetal hemoglobin may be especially usefulin the treatment of Sickle cell anemia. As such, the present inventionprovides improved methods for treating Sickle cell anemia.

In one embodiment, after a particular hemangio-colony forming cellpreparation is chosen to be suitable for a patient, it is thereafterexpanded to reach appropriate quantities for patient treatment anddifferentiated to obtain differentiated hematopoietic cells prior toadministering cells to the recipient. Methods of conducting apharmaceutical business may also comprise establishing a distributionsystem for distributing the preparation for sale or may includeestablishing a sales group for marketing the pharmaceutical preparation.

In any of the foregoing, hemangio-colony forming cells can be directlydifferentiated or hemangio-colony forming cells can be frozen for lateruse. In certain embodiments, the invention provides a frozen culture ofhemangio-colony forming cells suitable for later thawing and expansion,and also suitable for differentiation to hematopoietic or endotheliallineages.

Human hemangio-colony forming cells can be used to generate substantialnumbers of hematopoietic cell types that can be used in bloodtransfusions. For examples, substantial numbers of homogeneous orheterogeneous populations RBCs and/or platelets can be generated fromhuman hemangio-colony forming cells. Hemangio-colony forming cells andhematopoietic cell types differentiated therefrom can be banked, as iscurrently done with donated blood products, and used in transfusions andother treatments. Banking of these products will help alleviate thecritical shortage of donated blood products. Additionally,hemangio-colony forming cells and derivative products can be geneticallymanipulated in vitro to provide universal donor blood products.

As such, in certain aspects the invention provides a method ofconducting a blood banking business. The subject banking businessinvolves the derivation and storage (long or short term) ofhemangio-colony forming cells and/or hematopoietic cell types (e.g.,RBCs, platelets, lymphocytes, etc.) generated therefrom. Cells can becryopreserved for long term storage, or maintained in culture forrelatively short term storage. Cells can be typed and cross-matched inmuch the same way the currently available blood products are typed, andthe cells can be stored based on type. Additionally and in certainembodiments, cells can be modified to specifically generate cells thatare A negative and/or B negative and/or Rh negative to produce cellsthat are universally or nearly universally suitable for transfusion intoany patient.

Note that hemangio-colony forming cells and/or differentiatedhematopoietic cell types can be generated using any of the methods ofthe invention detailed through the specification.

In certain embodiments of a method of conducting a blood bankingbusiness, the cells (hemangio-colony forming cells and/or differentiatedhematopoietic cell types) are generated and stored at one or morecentral facilities. Cells can then be transferred to, for example,hospitals or treatment facilities for use in patient care. In certainother embodiments, cells are maintained in a cryopreserved state andspecifically thawed and prepared for transfusion based on orders fromhospitals or other treatment facilities. Such orders may be a standingorder (e.g., generate and provide a certain quantity of cells of acertain number of units

In certain embodiments, the method includes a system for billinghospitals or insurance companies for the costs associated with thebanked products.

In certain embodiments of any of the foregoing, the cells can beallocated based on cell number, volume, or any unit that permits theuser to quantify the dose being administered to patients and/or tocompare these doses to that administered during a standard bloodtransfusion.

In certain embodiments, the cells are generated, stored, andadministered as a mixed population of cells. For example, thepreparation may include cells of varying developmental stages, as wellas distinct cell types. In other embodiments, the cells are generated,stored, and/or administered as a substantially purified preparation of asingle cell type.

In certain embodiments, the preparations of cells are screened for oneor more infectious diseases. Screening may occur prior to or subsequentto generation or storage. For example, the preparations of cells may bescreened to identify hepatitis, HIV, or other blood-borne infectiousdisease that could be transmitted to recipients of these products.

Induction of Tolerance in Graft Recipients

The human hemangioblast cells generated and expanded by the methods ofthis invention, or expanded by the methods of this invention, may beused to induce immunological tolerance. Immunological tolerance refersto the inhibition of a graft recipient's immune response which wouldotherwise occur, e.g., in response to the introduction of a nonself MHCantigen (e.g., an antigen shared with the graft and the tolerizinghemangioblasts) into the recipient. Thus, tolerance refers to inhibitionof the immune response induced by a specific donor antigen as opposed tothe broad spectrum immune inhibition that may be elicited usingimmunosuppressants. Tolerance may involve humoral, cellular, or bothhumoral and cellular responses. Tolerance may include the eliminationand/or inactivation of preexisting mature donor-reactive T cells as wellas long-term (e.g. lifelong) elimination and/or inactivation of newlydeveloping donor-reactive T cells.

The methods described in the present invention of generating andexpanding human hemangioblasts offer several advantages for inducingtolerance. The methods of the present invention result in the generationof large, previously unobtainable numbers of human hemangioblasts. Largenumbers of human hemangioblasts allow induction of tolerance in graftrecipients with less toxic preconditioning protocols. Furthermore, themethods of the present invention provide for the generation of a libraryof human hemangioblasts, each of which is hemizygous or homozygous forat least one MHC allele present in the human population, wherein eachmember of said library of hemangioblast cells is hemizygous orhomozygous for a different set of MHC alleles relative to the othermembers in the library. Such a library of human hemangioblasts can beused in the selection of tolerizing human hemangioblast cells such thatcells can be selected to match any available donor graft.

Bone marrow transplantation and subsequent establishment ofhematopoietic or mixed chimerism have previously been shown to inducespecific tolerance to new tissue types derived from hematopoietic stemcells in both murine and human models. Hematopoietic or mixed chimerismrefers to the production in a recipient of hematopoietic cells derivedfrom both donor and recipient stem cells. Hence, if a recipient achieveshematopoietic chimerism, the recipient will be tolerant todonor-specific antigens. In many protocols for inducing tolerance, thetolerizing donor cells that are administered to the recipient engraftinto the bone marrow of the recipient. To create hematopoietic space inthe recipient bone marrow for the donor cells, some protocols require astep of creating hematopietic space (e.g., by whole body irradiation),and such a step is typically toxic or harmful to the recipient. However,if very large numbers of donor tolerizing cells are available, there isevidence from rodent models that irradiation can be completelyeliminated, thereby achieving hematopoietic or mixed chimerism with theadvantage of less toxic pre-conditioning regimens. Thus, mixed chimerismcan be achieved, for example, with specific, non-myeloablative recipientconditioning.

Accordingly, as the novel methods described herein enable the productionof large numbers of human hemangioblast cells, the present inventionoffers the advantage of inducing immune tolerance with less rigorous orless toxic conditioning protocols. For example, the hematopoieticspace-creating step may be eliminated if a sufficient number oftolerizing donor cells are used.

Accordingly, in certain embodiments of the present invention, humanhemangioblast cells generated and expanded or expanded by the methodsdescribed herein may be used to induce immunological tolerance. Whilenot wishing to be bound by any theory on the mechanism, the humanhemangioblast cells may induce immunological tolerance by homing to therecipient's bone marrow and engrafting into the recipient's bone marrowin order to produce mixed chimerism.

In certain embodiments, donor human hemangioblast cells are administeredto a recipient patient (e.g., by intravenous injection) prior toimplanting a graft or transplanting an organ, tissue, or cells from thedonor into the recipient patient. In certain embodiments, humanhemangioblasts are administered to induce tolerance in patients in needthereof (e.g., graft or transplant recipients). Accordingly, in certainembodiments the method of inducing tolerance in a human recipientpatient comprises the steps of: (a) selecting a patient in need of atransplant or cellular therapy; (b) administering to said patient humanhemangioblast cells derived from a donor or that are matched to thedonor, wherein said hemangioblast cells are generated and expanded orexpanded according to the methods of this invention, and (c) implantinga donor organ, tissue, or cell graft into the recipient patient, whereinsaid hemangioblast cells induce tolerance to donor antigens. In certainembodiments, the patient will receive an organ, tissue, or cell therapy,wherein the organ, tissue, or cells are obtained from the donor or adonor cell source. For example, hemangioblast cells from a donor can be(1) expanded according to the methods described herein to generate alarge number of donor tolerizing cells, and (2) expanded anddifferentiated in vitro to obtain hematopoietic or endothelial cells ortissues, which can be subsequently implanted into the recipient patient.In other embodiments, the organ, tissue, or cell therapy is not derivedfrom donor hemangioblast cells but is matched to the donorhemangioblasts.

As used herein, the term “matched” relates to how similar the HLA typingis between the donor and the recipient (e.g., graft). In one embodiment,the term “matched” with respect to donor hemangioblast cells and graftrefers to a degree of match t the MHC class I and/or at the MHC class IIalleles such that rejection does not occur. In another embodiment, theterm “matched” with respect to donor hemangioblasts and graft refers toa degree of match at the MHC class I and/or at the MHC class II allelessuch that the donor graft is tolerized by its matching donorhemangioblast cells. In another embodiment, the term “matched” withrespect to donor hemangioblast and graft refers to a degree of match atthe MHC class I and/or at the MHC class II alleles such thatimmunosuppression is not required.

The methods described herein for inducing tolerance to an allogeneicantigen or allogeneic graft may be used where, as between the donor andrecipient, there is degree of mismatch at MHC loci or other loci, suchthat graft rejection results. Accordingly, for example, in certainembodiments, there may be a mismatch at least one MHC locus or at leastone other locus that mediates recognition and rejection, e.g., a minorantigen locus. In some embodiments, for example, the HLA alleles of therecipient and donor are mismatched and result in one or more mismatchedantigens. With respect to class I and class II MHC loci, the donor andrecipient may be, for example: matched at class I and mismatched atclass II; mismatched at class I and matched at class II; mismatched atclass I and mismatched at class II; matched at class I, matched at classII. In any of these combinations other loci which control recognitionand rejection, e.g., minor antigen loci, may be matched or mismatched.Mismatched at MHC class I means mismatched for one or more MHC class Iloci, e.g., mismatched at one or more of HLA-A, HLA-B, or HLA-C.Mismatched at MHC class II means mismatched at one or more MHC class IIloci, e.g., mismatched at one or more of a DPA, a DPB, a DQA, a DQB, aDRA, or a DRB. For example, the hemangioblasts and the graft may bematched at class II HLA-DRB1 and DQB1 alleles. The hemangioblasts andgraft may further be matched at two or more class I HLA-A, B, or C,alleles (in addition to having matched DRB1 and DQB1 alleles).

In other embodiments, the tolerizing donor cells are cells derived fromthe hemangioblasts generated and expanded or expanded by the methodsdescribed herein. According to this embodiment, donor humanhemangioblasts are differentiated in vitro to give rise to donorhematopoietic stem cells, and the donor hematopoietic stem cells arethen administered to the recipient patient to induce tolerance. In anyof the above methods, the donor hemangioblasts or hematopoietic stemcells derived therefrom and administered to said recipient prepare therecipient patient for the matched (with respect to the donor tolerizingcells) transplant or graft by inducing tolerance in said recipient.

In other embodiments, the method of inducing tolerance further comprisesthe step(s) of creating hematopoietic space (to promote engraftment ofhemangioblasts or hematopoietic stem cells derived therefrom). Inanother embodiment, the method of inducing tolerance further comprisesthe step(s) of temporarily inhibiting rejection of donor hemangioblastcells or hematopoetic stem cells derived therefrom by, for example,eliminating and/or inactivating preexisting donor-reactive T cells. Inorder to create hematopoietic space, the method may include irradiation(e.g., whole body, lymphoid, or selective thymic irradiation). Toprevent rejection of donor cells, the method may further comprise theadministration of drugs or antibodies (e.g., inhibitors of cellproliferation, anti-metabolites, or anti-T cell or anti-CD8 or anti-CD4antibodies), and/or other treatments that promote survival andengraftment of the donor cells and the formation of mixed chimerism(e.g., the administration of stromal cells or growth factors, cytokines,etc. to said recipient, or other agents that deplete or inactive therecipient's natural antibodies). In certain embodiments, theirradiation, antibodies, drugs, and/or other agents administered tocreate hematopoietic space and/or promote survival of donor cells in therecipient, is sufficient to inactivate thymocytes and/or T cells in therecipient. Such a step of creating hematopoietic space and/ortemporarily inhibiting rejection of donor cells may be performed, forexample, before the introduction of the donor hemangioblast cells tosaid recipient. Alternatively, the patient may receive an agent ormethod for blocking, eliminating, or inactivating T cells concurrentlywith the administration of the donor tolerizing cells.

In certain embodiments, a combination of hematopoietic space-creatingand immunosuppressive methods are used. For example, a recipient mayreceive an anti-T cell antibody in combination with low dose whole bodyirradiation and/or thymic irradiation. In one embodiment, the recipientmay receive anti-CD4 and anti-CD8 antibodies, followed by a mild,nonmyeloablative dose of whole body irradiation (e.g., a dose thateliminates a fraction of the recipient's bone marrow without renderingthe bone marrow unrecoverable) and selective thymic irradiation oralternatively, an additional dose of T cell-inactivating antibodies orcostimulatory blocking reagents (e.g., CTLA4-Ig and/or anti-CD40Lantibody). Following the irradiation, donor hemangioblast cells, orhematopoietic stem cells derived therefrom, may be administered to therecipient (e.g., by intravenous injection). In this embodiment, wholebody irradiation to promote engraftment of donor cells may be replacedby administering a large number of donor human hemangioblasts orhematopoietic stem cells derived therefrom. Obtaining such large numbersof donor human cells can be achieved according to the methods describedherein.

In another embodiment, treatments to deplete or inactivate recipient Tcells may help to prevent inhibition of engraftment or promote survivalof the administered donor tolerizing human hemangioblast cells. Inanother embodiment, the method may include clonal deletion ofdonor-reactive cells in the recipient patient. For example, a patientmay receive a mild dose of whole body irradiation, followed byadministration of donor human hemangioblasts and T cell costimulatoryblockade. Alternatively, a patient may receive T cell costimulatoryblockade and administration of large numbers of donor humanhemangioblast cells without receiving irradiation.

In another embodiment, tolerance may be achieved without myeloablativeconditioning of the recipient. In one embodiment, a recipient mayreceive donor human hemangioblasts in combination with anti-CD40L tofacilitate engraftment of donor hemangioblasts. For example, a recipientmay receive large numbers of donor hemangioblasts, along with anti-CD40Lmonoclonal antibody, followed within a few days by a dose of CTLA4-Ig.Such a protocol may delete donor-reactive T cells and block theCD40-CD40L interaction. The novel methods described herein forgenerating and expanding human hemangioblasts in vitro render such amild tolerance protocol feasible.

Following recipient conditioning and/or depletion or blocking ofdonor-reactive T cells, donor tolerizing human hemangioblasts generatedby the methods of the present invention are administered to therecipient. Donor human hemangioblasts may be derived from hemangioblastsobtained from a tissue or cell source from the donor. Alternatively,donor human hemangioblasts may be obtained from a different non-donorsource that is matched to the donor.

In certain embodiments, tolerance is induced in a recipient patient byadministering donor human hemangioblasts in multiple administrations(e.g., by two, three, four, or more administrations of the donor cells).Accordingly, tolerance may be induced by a method comprising multipleadministrations of donor tolerizing cells, wherein the multipleadministrations are given to the recipient within a timeframe of a weekor less.

In certain embodiments, the ability of the human hemangioblast cells ofthis invention to induce immunological tolerance may be evaluated usingdifferent experimental model systems. For example, the ability toestablish a human immune system in a SCID mouse has been used to studythe human immune response in an experimental model. It has beenpreviously shown that human fetal liver and thymus tissue may be used toreconstitute a functional human immune system in an immuno-incompetentmouse recipient. Similarly, the functional capacity of the humanhemangioblast cells of this invention can be assessed using a similarexperimental model system. For example, the ability of humanhemangioblasts to replace human fetal liver in establishing a functionalhuman immune system in the mouse can be evaluated using theabove-described experimental model. Further, in a mouse with afunctional human immune system (e.g., where a human fetal liver andthymus tissue is used to establish a human immune system in a SCID mouseto produce a hu-SCID mouse), human “donor” hemangioblasts (mismatchedwith respect to the fetal liver and thymic tissue used to establish thehu-SCID mouse) may be administered to the hu-SCID mouse, according toany of the methods described above, in order to achieve mixed chimerism.Tolerance to donor antigen can be subsequently tested upon implantationof an allograft matched with respect to the donor hemangioblasts intothese animals.

In certain embodiments, the present invention relates to cellcombinations. Effective cell combinations comprise two components: afirst cell type to induce immunological tolerance, and a second celltype that regenerates the needed function. Both cell types may beproduced by the methods of the present invention and obtained from thesame donor. For example, human hemangioblast cells from a donor may beused as the tolerizing donor cells. Cells from the donor (e.g.,embryonic stem cells, pluripotent stem cells or early progenitor cells,or hemangioblasts) may also be used to generate, for example,hematopoietic cells or endothelial cells (as described herein), neuralcells such as oligodendrocytes, hepatocytes, cardiomyocytes orcardiomyocyte precursors, or osteoblasts and their progenitors.Accordingly, the donor human hemangioblasts may be used to inducetolerance in a recipient such that the recipient is tolerant to cells ortissues derived from said donor hemangioblast cells or from said donorembryonic or pluripotent stem cells.

In another embodiment, the two cell components of the cell combinationsof the present invention may be obtained from different sources ordonors, wherein the two sources or donors are matched. For example,hemangioblasts may be generated from an embryonic stem cell source,whereas the graft cells or tissues may be obtained from a source that isdifferent from the embryonic stem cell source used to generate the humanhemangioblasts. In such embodiments, the two sources are matched.

For any of the therapeutic purposes described herein, humanhemangioblast or hematopoietic cells derived therefrom forimmunotolerance may be supplied in the form of a pharmaceuticalcomposition, comprising an isotonic excipient prepared undersufficiently sterile conditions for human administration.

Hemangioblasts in Gene Therapy

Other aspects of the invention relate to the use of hemangioblast cells,or hematopoietic or endothelial cells differentiated therefrom, or inturn cells further differentiated from these cells, in gene therapy. Thepreparation of mammalian hemangioblast cells of the invention may beused to deliver a therapeutic gene to a patient that has a conditionthat is amenable to treatment by the gene product of the therapeuticgene. The hemangioblasts are particularly useful to deliver therapeuticgenes that are involved in or influence angiogenesis (e.g VEGF to induceformation of collaterals in ischemic tissue), hematopoiesis (e.g.erythropoietin to induce red cell production), blood vessel function(e.g. growth factors to induce proliferation of vascular smooth musclesto repair aneurysm) or blood cell function (e.g. clotting factors toreduce bleeding) or code for secreted proteins e.g. growth hormone.Methods for gene therapy are known in the art. See for example, U.S.Pat. No. 5,399,346 by Anderson et al. A biocompatible capsule fordelivering genetic material is described in PCT Publication WO 95/05452by Baetge et al. Methods of gene transfer into bone-marrow derived cellshave also previously been reported (see U.S. Pat. No. 6,410,015 byGordon et al.). The therapeutic gene can be any gene having clinicalusefulness, such as a gene encoding a gene product or protein that isinvolved in disease prevention or treatment, or a gene having a cellregulatory effect that is involved in disease prevention or treatment.The gene products may substitute a defective or missing gene product,protein, or cell regulatory effect in the patient, thereby enablingprevention or treatment of a disease or condition in the patient.

Accordingly, the invention further provides a method of delivering atherapeutic gene to a patient having a condition amenable to genetherapy comprising, selecting the patient in need thereof, modifying thepreparation of hemangioblasts so that the cells carry a therapeuticgene, and administering the modified preparation to the patient. Thepreparation may be modified by techniques that are generally known inthe art. The modification may involve inserting a DNA or RNA segmentencoding a gene product into the mammalian hemangioblast cells, wherethe gene enhances the therapeutic effects of the hemangioblast cells.The genes are inserted in such a manner that the modified hemangioblastcell will produce the therapeutic gene product or have the desiredtherapeutic effect in the patient's body. In one embodiment, thehemangioblasts are prepared from a cell source originally acquired fromthe patient, such as bone marrow. The gene may be inserted into thehemangioblast cells using any gene transfer procedure, for example,naked DNA incorporation, direct injection of DNA, receptor-mediated DNAuptake, retroviral-mediated transfection, viral-mediated transfection,non-viral transfection, lipid-mediated transfection, electrotransfer,electroporation, calcium phosphate-mediated transfection, microinjectionor proteoliposomes, all of which may involve the use of gene therapyvectors. Other vectors can be used besides retroviral vectors, includingthose derived from DNA viruses and other RNA viruses. As should beapparent when using an RNA virus, such virus includes RNA that encodesthe desired agent so that the hemangioblast cells that are transfectedwith such RNA virus are therefore provided with DNA encoding atherapeutic gene product. Methods for accomplishing introduction ofgenes into cells are well known in the art (see, for example, Ausubel,id.).

In accordance with another aspect of the invention, a purifiedpreparation of human hemangioblast cells, in which the cells have beenmodified to carry a therapeutic gene, may be provided in containers orcommercial packages that further comprise instructions for use of thepreparation in gene therapy to prevent and/or treat a disease bydelivery of the therapeutic gene. Accordingly, the invention furtherprovides a commercial package (i.e., a kit) comprising a preparation ofmammalian hemangioblast cells of the invention, wherein the preparationhas been modified so that the cells of the preparation carry atherapeutic gene, and instructions for treating a patient having acondition amenable to treatment with gene therapy.

Other Commercial Applications and Methods

Certain aspects of the present invention pertain to the expansion ofhuman hemangioblasts to reach commercial quantities. In particularembodiments, human hemangioblasts are produced on a large scale, storedif necessary, and supplied to hospitals, clinicians or other healthcarefacilities. Once a patient presents with an indication such as, forexample, ischemia or vascular injury, or is in need of hematopoieticreconstitution, human hemangioblasts can be ordered and provided in atimely manner. Accordingly, the present invention relates to methods ofgenerating and expanding human hemangioblasts to attain cells on acommercial scale, cell preparations comprising human hemangioblastsderived from said methods, as well as methods of providing (i.e.,producing, optionally storing, and selling) human hemangioblasts tohospitals and clinicians. Further, hemangioblast lineage cells may beproduced in vitro and optionally stored and sold to hospitals andclinicians.

Accordingly certain aspects of the present invention relate to methodsof production, storage, and distribution of hemangioblasts expanded bythe methods disclosed herein. Following human hemangioblast generationand expansion in vitro, human hemangioblasts may be harvested, purifiedand optionally stored prior to a patient's treatment. Alternatively, insituations in which hemangioblast lineage cells are desired, humanhemangioblasts may be differentiated further in vitro prior to apatient's treatment. Thus in particular embodiments, the presentinvention provides methods of supplying hemangioblasts to hospitals,healthcare centers, and clinicians, whereby hemangioblasts orhemangioblast lineage cells produced by the methods disclosed herein arestored, ordered on demand by a hospital, healthcare center, orclinician, and administered to a patient in need of hemangioblast orhemangioblast lineage therapy. In alternative embodiments, a hospital,healthcare center, or clinician orders human hemangioblasts based onpatient specific data, human hemangioblasts are produced according tothe patient's specifications and subsequently supplied to the hospitalor clinician placing the order.

Further aspects of the invention relate to a library of hemangioblastsand/or hemangioblast lineage cells that can provide matched cells topotential patient recipients. Accordingly, in one embodiment, theinvention provides a method of conducting a pharmaceutical business,comprising the step of providing hemangioblast preparations that arehomozygous for at least one histocompatibility antigen, wherein cellsare chosen from a bank of such cells comprising a library of humanhemangioblasts that can be expanded by the methods disclosed herein,wherein each hemangioblast preparation is hemizygous or homozygous forat least one MHC allele present in the human population, and whereinsaid bank of hemangioblast cells comprises cells that are eachhemizygous or homozygous for a different set of MHC alleles relative tothe other members in the bank of cells. As mentioned above, genetargeting or loss of heterozygosity may be used to generate thehemizygous or homozygous MHC allele stem cells used to derive thehemangioblasts. In one embodiment, after a particular hemangioblast cellpreparation is chosen to be suitable for a patient, it is thereafterexpanded to reach appropriate quantities for patient treatment. Suchmethods may further comprise the step of differentiating thehemangioblasts to obtain hematopoietic and/or endothelial cells prior toadministering cells to the recipient. Methods of conducting apharmaceutical business may also comprise establishing a distributionsystem for distributing the preparation for sale or may includeestablishing a sales group for marketing the pharmaceutical preparation.

Other aspects of the invention relate to the use of the humanhemangioblasts of the present invention as a research tool in settingssuch as a pharmaceutical, chemical, or biotechnology company, ahospital, or an academic or research institution. For example, humanhemangioblasts and hemangioblast derivative cells (e.g., endothelialcells) may be used to screen and evaluate angiogenic and anti-angiogenicfactors or may be used in tissue engineering. In addition, because thehemangioblasts obtained and expanded by the methods disclosed hereinhave dual potential to differentiate into hematopoietic and endothelialcells, they may be used for the cellular and molecular biology ofhematopoiesis and vasculogenesis. Further, the human hemangioblasts maybe used for the discovery of novel markers of these cells, genes, growthfactors, and differentiation factors that play a role in hematopoiesisand vasculogenesis, or for drug discovery and the development ofscreening assays for potentially toxic or protective agents.

In other embodiments of the present invention, hemangioblast lineagecells (such as blood cells) are also used commercially. Hematopoieticcells may be used to generate blood products, such as hemoglobin andgrowth factors, that may be used for clinical and research applications.

The present invention also includes methods of obtaining human ES cellsfrom a patient and then generating and expanding human hemangioblastsderived from the ES cells. These hemangioblasts may be stored. Inaddition, these hemangioblasts may be used to treat the patient fromwhich the ES were obtained or a relative of that patient.

As the methods and applications described above relate to treatments,pharmaceutical preparations, and the storing of hemangioblasts, thepresent invention also relates to solutions of hemangioblasts that aresuitable for such applications. The present invention accordinglyrelates to solutions of hemangioblasts that are suitable for injectioninto a patient. Such solutions may comprise cells formulated in aphysiologically acceptable liquid (e.g., normal saline, buffered saline,or a balanced salt solution). A solution may optionally comprise factorsthat facilitate cell differentiation in vivo. A solution may beadministered to a patient by vascular administration (e.g., intravenousinfusion), in accordance with art accepted methods utilized for bonemarrow transplantation. In some embodiments, the cell solution isadministered into a peripheral vein, a superficial peripheral vein, oralternatively, by central venous administration (e.g., through a centralvenous catheter). The number of cells in the solution may be at leastabout 10² and less than about 10⁹ cells. In other embodiments, thenumber of cells in the solution may range from about 10¹, 10², 5×10²,10³, 5×10³, 10⁴, 10⁵, 10⁶, 10⁷, or 10⁸ to about 5×10², 10³, 5×10³, 10⁴,10⁵, 10⁶, 10⁷, 10⁸, or 10⁹, where the upper and lower limits areselected independently, except that the lower limit is always less thanthe upper limit. Further, the cells may be administered in a single orin multiple administrations.

The present invention will now be more fully described with reference tothe following examples, which are illustrative only and should not beconsidered as limiting the invention described above.

Example 1 Hemangioblasts Derived from Human ES Cells Exhibit BothHematopoietic and Endothelial Potential

The human embryonic stem cell lines H1 and H9 are cultured in ES cellmedia with mouse embryonic fibroblasts (MEFs). Cultured human ES cellsare detached, pelleted by centrifugation at 200 g, and resuspended inembryoid body (EB) formation medium. EB formation medium comprisesserum-free Stemline media (Sigma®) supplemented with BMP-4 and VEGF.Cells are then plated on ultra-low attachment culture dishes andcultured in a CO₂ incubator. After 24-48 hours, early hematopoieticcytokines (TPO, Flt-3 ligand, and SCF) are added and the cells incubatedfor another 24-48 hours to form EBs.

Embryoid bodies (EB) are cultured for 2-6 days or optionally 2-5 daysand then collected, washed with PBS and disaggregated into single cellsuspensions using Trypsin/EDTA. The numbers of EBs are determined andapproximately 5-10×10⁶ cells/mL are cultured in serum-freemethylcellulose medium that is optimized for hemangioblast growthcomprising BL-CFU medium (Stem Cell Technology′) and that issupplemented with cytokines and a PTD-HOXB4 fusion protein. The cellsare then replated onto a new ultra-low attachment culture dish to allowthe growth of hemangioblast colonies.

The EBs are monitored daily for the formation of hemangioblast colonies.At approximately 3 days, the formation of hemangioblast colonies areobserved. The hemangioblasts are characterized by a very distinctivegrape-like cell morphology.

Some of the cells should be able to form EBs again (secondary EBs). Thesecondary EBs do not have grape-like morphology, as shown in FIG. 16b .The hemangioblasts are also smaller than the secondary EBs.

These hemangioblast colonies are then selected, picked and replated intomethylcellulose CFU-medium to test for their capacity to furtherdifferentiate and form hematopoietic colony-forming units (CFUs).Similarly, these hemangioblast colonies are selected, picked andreplated onto fibronectin-coated culture plates optimized for the firststep towards endothelial differentiation.

To test for the generation of hematopoietic progenitor cells from theseselected hemangioblast colonies, the growth of colony-forming units(CFU) for granulocytes, erythrocytes, macrophages and megakaryocytes aremeasured during the next 3-10 days of growth.

To test for the generation of endothelial cells from these isolatedhemangioblast colonies, the ability of the hemangioblasts to formbranched tube-cords when they are replated into thick layers of Matrigelis examined.

The ability of the isolated hemangioblast colonies to differentiate intoendothelial cells could also be confirmed using otherendothelial-specific assays, such as LDL uptake or the presence ofendothelial cell surface markers.

Example 2 Additional Characterization of hESC-Derived BC Cells orHemangioblasts

Human ES Cell Culture.

The hES cell lines used in this study were previously described HI, H7,and H9 (NIH-registered as WA01, WA07, and WA09) cell lines and fourlines (MA01, MA03, MA40, and MA09) derived at Advanced Cell Technology.Undifferentiated human ES cells were cultured on inactivated (mitomycinC-treated) mouse embryonic fibroblast (MEF) cells in complete hES mediauntil they reached 80% confluence (Klimanskaya & McMahon; Approaches ofderivation and maintenance of human ES cells: Detailed procedures andalternatives, in Handbook of Stem Cells. Volume 1: Embryonic Stem Cells,ed. Lanza, R. et. al. (Elsevier/Academic Press, San Diego, 2004). Thenthe undifferentiated hES cells were dissociated by 0.05% trypsin-0.53 mMEDTA (Invitrogen™) for 2-5 min and collected by centrifugation at 1,000rpm for 5 minutes.

EB Formation.

To induce hemangioblast precursor (mesoderm) formation, hES cells (2 to5×10⁵ cells/ml) were plated on ultra-low attachment dishes (Corning™) inserum-free Stemline media (for e.g., Stemline I or II, Sigma™) with theaddition of BMP-4 and VEGF₂₆₅ (50 ng/ml, R&D Systems™) and cultured in5% CO₂. Approximately 48 hours later, the EB medium was replenished andsupplemented with a cocktail of early hematopoietic/endothelial growthfactors. For example, half the media were removed 48 hours later andfresh media were added with the same final concentrations of BMP-4 andVEGF, plus SCF, TPO and FLT3 ligand (20 ng/ml, R&D Systems). The tripleprotein transduction domain (tPTD)-HoxB4 fusion protein (1.5 μg/ml) wasadded to the culture media between 48-72 hr to expand the hemangioblastsand their precursors.

Hemangioblast or Blast Cell Expansion.

After 3.5-5 days, EBs were collected and dissociated by 0.05%trypsin-0.53 mM EDTA (Invitrogen™) for 2-5 min, and a single cellsuspension was prepared by passing through 22 G needle 3-5 times and a40 μM strainer. Cells were collected by centrifugation at 1,000 rpm for5 minutes and counted. Cell pellets were resuspended in 50-200 μl ofserum-free Stemline media. To expand hemangioblasts, single cellsuspensions from EBs derived from differentiation of 2 to 5×10⁵ hEScells were mixed with 2 ml BL-CFC/hemangioblast expansion media (BGM)containing 1.0% methylcellulose in Iscove's MDM, 1-2% Bovine serumalbumin, 0.1 mM 2-mercaptoethanol and a cocktail of growth factors. Forexample, 10 μg/ml rh-Insulin, 200 μg/ml iron saturated humantransferrin, 20 ng/ml rh-GM-CSF, 20 ng/ml rh-IL-3, 20 ng/ml rh-IL-6, 20ng/ml rh-G-CSF, 3 to 6 units/ml rh-EPO, 50 ng/ml rh-SCF, 50 ng/mlrh-FLt3 ligand, 50 ng/ml rh-VEGF and 50 ng/ml rh-BMP-4) (“rh” stands for“recombinant human”) and 1.5 μg/ml of tPTD-HoxB4 fusion protein,with/without 50 ng/ml of TPO and FL, was added. The cell mixtures wereplated on ultra-low attachment dishes (e.g., 2-5×10⁵ cells/2 ml in onewell of a six-well plate) and incubated at 37° C. in 5% CO₂ for 4-7days. After 4-6 days, grape-like hemangioblast blast colonies (referredto as BL-CFCs or BCs) were visible by microscopy, as shown in FIG. 16 a.

Approximately 0.35±0.01% and 0.52±0.06% of individual cells from WA01hES cells and MA01 hES cells developed into grape-like blast colonies(BCs), respectively. The BCs contained <10 cells at the beginning of day3, rapidly expanding from days 4 to 6 to >100 cells (FIG. 16a ). Thecolonies were generally less compact and more morphologically homogenousthan secondary EBs (FIG. 16b ). Cytospin preparation and Wright-Giemsastaining of the hES-derived blast colonies confirmed morphologicfeatures of immature blast cells (FIG. 16c ). To extend these results toother hES cell lines (WA07 [H7], WA09 [H9], MA01, MA03, MA09, and MA40),supplements of FL (50 ng/ml) and Tpo (50 ng/ml) were necessary forsustained growth of the BC colonies (without FL and Tpo, small (10-20cell) hES-BCs were obtained which died after 4-8 days). The discrepancyobserved between different hESC lines may be due to the instrinsicproperties of these cell lines as previously observed by Bowles et al.(2006 Stem Cells 24: 1359-1369). Epo (3-6 units/ml of human recombinantEpo) was also essential for BC formation and growth in all hES celllines tested.

A time course was examined (from 2 days to 6 days) of human BL-CFCformation in EBs, and a narrow time period was found during which humanESC-derived EBs generated the greatest numbers of BL-CFCs (or hES-BCs).Day 2 EBs generated hES-BCs at a low frequency (57.3±7.4 BCs/1×10⁵ EBcells for WA01 hES cells, mean±SE, n=3; 395±10.4 BCs/1×10⁵ EB cells forMA01 hES cells, n=3), and by day 6 only gave rise to hematopoietic(erythroid) progenitors. However, day 3.5 EBs generated large numbers ofhemangioblasts or hES-BCs (347.4±11.1 BCs/1×10⁵ EB cells for WA01 hEScells, n=3; 523.3±60.1 BCs/1×10⁵ EB cells for MA01 hES cells, n=3) inall hESC lines tested, including hESC lines derived from bothblastocysts (WA01 and WA09) and single blastomeres (MA01 and MA09).Although efficiencies depended on the hESC line and growth conditions(see Table 1), one E-well plate of WA01-GFP and MA01 hES cells(12-13×10⁶ cells) generated approximately 22.18±3.51×10⁶ (expanded for6-8 days, mean±SE, n=17), and 49.73±7.23×10⁶ (expanded for 6-8 days,n=9) and 396.4±91.63×10⁶ (expanded for 10-13 days, n=6) hemangioblast orhES-BC cells, respectively. Accordingly, the cells could be readilyexpanded under the well-defined and reproducible conditions describedabove.

TABLE 1 Efficiency of hES-BC cells derived from different hES cell lineshES cell lines hES-BC cells (10⁵)*/1 × 10⁶ hES cells WA01(H1) 11.7;26.7; 8.4; 20.0; 22.8; 31.9; 27.5; 8.4; 10.0; 16.7; 8.8; 14.2; 9.4; 7.5;10.0; 52.5; and 28.0 (17 experiments)* WA07 (H7) 6.5 and 17.0 (2experiments)* WA09 (H9) 1.8; 2.0; and 2.2 (3 experiments)* MA01 22.5;25.0; 45.0; 42.5; 32.5; 42.8; 27.1; 80.0; and 55.5 (9 experiments)*156.7; 220.8; 437.5; 192.0; 325.0; and 650.0 (6 experiment)# MA09 6.5and 11.3 (2 experiments)* MA40 2.2; 2.5; and 3.0 (3 experiments)**hES-BC cells were collected and purified after culturing in BGM for 6-8days, then the number of cells was counted using a hemocytometer. Theefficiency was calculated based on 2 × 10⁶ cells/well of hES cells in astandard 6-well plate. #BCs were expanded for 10-13 days.

Cryopreservation of Hemangioblasts.

Hemangioblasts (or blast cells or hES-BC cells) can be cryopreservedwith serum-free media. For cryopreservation of hemangioblast cells,purified cells were divided into two identical portions: half of thesecells were directly plated for both hematopoietic CFU assay andendothelial cell development, the other half was resuspended in 8% DMSOwith Stemline medium and stored in liquid nitrogen. Then cells werethawed and examined for hematopoietic and endothelial developmentpotentials. After thawing, the hemangioblast cells were plated for bothhematopoietic and endothelial lineage development as described hereinand compared with fresh, purified cells. For endothelial cell lineage,78±2% (mean±SE, n=3) of cells were recovered after the freezing process,while 61±7% (n=3) of total hematopoetic CFUs and 46±4% (n=3) ofCFU-erythroid were retained as compared to fresh hES-BC cells. No lossof more primitive multipotential progenitors for CFU-mix was observedafter recovering hES-BC cells from liquid nitrogen storage.

Characterization of Hemangioblasts.

For BL-CFC immunocytochemical analysis, purified BL-CFCs were cytospunonto polylysine treated glass slides and fixed in 4% paraformaldehyde.For examining the expression of most genes, primary antibodies wereincubated at 4° C. overnight, followed by fluorescent dye labeledsecondary antibodies, and finally examined under fluorescent microscope.Normal human BM cells, K562 cells and HUVEC were used as controls.

Immunocytochemical analysis revealed that the hES cell-derived BL-CFCsor BCs expressed several hemangioblast related proteins but no CD31,CD34 and KDR, or other adhesion molecules. The hES-BCs expressed GATA-1(FIGS. 16d and 16e ) and GATA-2 proteins. GATA-1 is a zinc fingertranscription factor essential for both primitive (embryonic) anddefinitive (adult) erythropoiesis and is expressed in murinehemangioblastic cells (Ferreira et al. 2005 Mol Cell Biol 25: 1215-1227and Yokomizo et al. 2007 EMBO J 26: 184-196). GATA-2 is a zinc fingertranscription factor that functions at multiple steps in hemangioblastdevelopment and differentiation (Lugus et al. 2007 Development 134:393-405)). The hES cell-derived BL-CFCs or BCs also expressed LMO2 (aLIM-domain protein critical for hemangioblast development (Gering et al.2003 Development 130: 6187-6199) (FIGS. 16g and 16h ) and CXCR-4 (FIGS.16n and 16o ). CXCR-4 is the receptor for chemokine SDF-1, which isexpressed on the surface of endothelial cells derived from hESCs,hematopoietic stem cells, and mouse hemangiocytes. CXCR-4 plays animportant role in the migration, retention, and development ofhematopoietic progenitors in the bone marrow. The cells additionallyexpressed TPO and EPO receptors (FIGS. 16t and 16u, and 16q and 16r ,and Table 1), and readily reacted with antibody specific for CD71, thetransferrin receptor (FIGS. 16j and 16k ) (see Table 2 and FIG. 16d-v ).The cells expressed little or no CD31, CD34 and KDR, or other adhesionmolecules (Table 2). The absence of CD34, CD31, and KDR expression, andthe absence of CD133 expression, is a unique profile of surface markerexpression.

For gene profiling analysis, total RNA was isolated from purifiedBL-CFCs/hES-BC cells, 3.5 day-EBs and undifferentiated ES cells usingthe RNAeasy kit (Qiagen). Fragmented antisense cRNA was used forhybridizing with human U133.2 arrays (Affymetrix®, Inc) at the CoreGenomic Facility of University of Massachusetts (Worcester, Mass.). Forexpression profiling of the β-cluster globin genes, individual CFUcolonies were picked up, RNA was isolated and amplified, and β-, γ- andε-globin gene expression was analyzed as described previously (Lu et al.2004 Blood (103): 4134-4141).

Molecular profiling by Affymetrix™ Arrays indicated a significantincrease in genes associated with hemangioblast and early primitiveerythroblast development as compared to early-stage EBs (Table 2). SCLand LMO2, two genes critical for hemangioblast development (D'Souza etal. 2005 Blood (105): 3862-3870; Park et al. 2004 Development (131):2749-2762; Gering et al. 2003 Development (130): 6187-6199)), as well asFLT-1 (a receptor for VEGF) were readily detectable in the BL-CFCs/blastcolonies. Embryonic (ε-globin, 549-fold) and fetal (γ-globin, 817-fold)globin gene expression was dramatically increased in theBL-CFCs/hES-BCs; NF-E2 (12-fold), GATA-1 (6-fold), EKLF (7-fold), ICAM-4(4-fold), glycophorins (14-fold) and Epo receptor (4-fold) messagelevels were also moderately increased.

TABLE 2 Characterization of BL-CFC (hES-BCs) by Affymetrix Arrays andImmunocytochemistry Affymetrix Arrays Immunocytochemistry BL- BL- GenesEBs CFC Antibodies CFC Hemangioblasts GATA-1 + GATA-2 + TAL1/SCL − +β-catenin + LMO2 + +↑ CXCR-4 + GATA-2 + + Tpo-receptor + FLT1 − +Epo-receptor + EGR-1 + HSC and Erythrioblast CD71 (transferrinreceptor) + Neurokinin B1 + Epo-receptor + +↑ KDR − c-Kit + − PECAM-1(CD31) − CXCR-4 + + VE-cadherin − GATA-1 − + CD34 − NF-E2 − + OCT-4 −EKLF − + Nanog − ICAM4 (CD242) − + TRA-I-88 − Band3 (CD233) − + SSEA-4 −Band7.2 + − CD41 − Glycophorins − + CD43 − Arkrin-1 − + Integrin α4 ±c-Myc + +↑ Integrin β1 ± ε-Globin − + γ-Globin − + PF-4 − + PDGF-R2(CD140A) + − Pim-1 + +↑ Endothelial Cell Tie-2 + − VE-cadherin − +MADCAM1 − + DOC1 − + EZFIT − + Integrin β3 (CD61) − + Selectin-P (CD62)− + VEGF + − Undifferentiated ES Cell OCT-4 + − TRA-1 + +↓ Wnt5a + −FGF-R + +↓ FGF-R2 + − FGF-R3 + − Mesoderm BMP-4 + − BMP-2 + − BMP-7 − +BMP-R1A + − AVC-R2B + +↓ MEST + +↓ Brunchy T + − Adhesion moleculesE-cadherin + − P-cadherin + − N-cadherin + +↓ Integrin β5 + − Integrinβ1 + +↓ Connexin 43 + +↓ For immunochemistry: +, moderate to strongstaining; −, negative staining; ±, very weak staining. For AffymetrixArrays: +, expression level above background; −, expression level belowbackground; +↑, expression level in BL-CFC is higher than expressionlevel in EBs; +↓, expression level in BL-CFC is lower than expressionlevel in EBs.

Functional Characterization of Hemangioblasts.

The grape-like hemangioblast colonies were picked and isolated manuallyunder dissection microscope and resuspended in serum-free Stemline(Stemline I) media. The cells were then tested for lineage potential bythe methods described below.

Clonality of hES-Blast Cells.

To determine whether hES-blast colonies were clonal and originated froma common bipotential progenitor cell, cell mixing experiments wereperformed as previously described in mouse studies (Choi et al. 1998Development (125): 725-732; Kennedy et al. 1997 Nature (386): 488-493).Cells from EBs of WA01-GFP and MA01 hES cells were mixed and plated inBGM. hES-blast colonies were examined 4-6 hours later by phase andfluorescence microscopy. In a series of three experiments, 100% (77 outof 77) of the blast colonies were found to be either GFP positive or GFPnegative (no mixed BCs were observed, FIGS. 18a and 18b ).

To rule out the possibility that the GFP negative colonies containedcells with an inactive GFP gene, GFP positive and GFP negative colonieswere examined for the presence of GFP sequence. Twelve individual GFPpositive and twelve individual GFP negative colonies from the mixingexperiments were handpicked under phase and fluorescence microscopy.Genomic DNA was isolated by a MicroDNA kit (Qiagen™), and GFP specificPCR reactions were performed. As an internal control for the PCRreactions, myogenin primers were included in all PCR reactions, whichgenerate a fragment of 245 bp. PCR products were separated on a 2%agarose gel and visualized by ethidium bromide staining. The polymerasechain reaction (PCR) analysis confirmed the absence of the GFP genesequence in all negative colonies (FIG. 18, PCR analysis)).

Dilution studies further confirmed the clonogenicity of both primary andsecondary BCs (Table 3, FIG. 18c ). Limited dilution studies werecarried out using different numbers of cells (from 1.5×10³ to 1.5×10⁴)from differentiated EBs. After diluting single EB-cell suspensions with150 ml BGM (100 cells/ml), they were plated in 15 ultra-low 96-wellplates and incubated at 37° C. for BC development. To confirm the clonalorigin of blast colonies, the plates were checked under maskedconditions by two associates 4 hours after plating. Wells with double ortriple cell clumps were excluded from further investigation.

As reported by Kennedy et al. (1997 Nature 386: 488-493) in mouse EScell studies, human blast colony (hES-BC or BC) development was alsocell density dependent with poor development at low cell number. SevenBCs developed from fifteen 96-well plates (FIG. 18c ). Additionallimiting dilution studies were performed to determine whether the BCscontained cells that have the potential to generate secondary BCs.

For secondary BC growth, primary blast colonies were handpicked anddissociated into single cells. The single cells were then mixed (200,300, and 1000 cells, respectively) with 20 ml BGM to make serialdilutions and plated in six ultra-low 96-well plates (0.1 ml/well).Wells with double or triple cell clumps were excluded from the study. Atotal of 29 secondary BCs with identical morphological characteristicsas primary BCs developed from five 96-well plates. These experimentsconfirmed the clonogenicity of both primary and secondary hES-BCs (Table3).

Bipotential Capacity of hES-Blast Colonies.

Two strategies were used to demonstrate the bipotential capacity ofclonally-derived blast cells. In the first method, for single BCexpansion, individual hES-BC colonies were handpicked and transferred toa fibronectin-coated 48-well plate containing Stemline II with growthfactors supporting the growth of hematopoietic and endothelial lineages.The growth factors in the liquid cultures included recombinant human SCF(20 ng/ml), Tpo (20 ng/ml), FL (20 ng/ml), IL-3 (20 ng/ml) VEGF (20ng/ml), G-CSF (20 n ng/ml), BMP-4 (15 ng/ml), IL-6 (10 ng/ml), IGF-1 (10ng/ml), endothelial cell growth supplement (ECGS, 100 μg/ml) and Epo (3U/ml). Following one week in culture, non-adherent hematopoietic cellswere removed by gentle pipetting and used directly for hematopoietic CFUassay. Following removal of the non-adherent cells, the adherentpopulations were cultured for one more week in EGM-2 endothelial cellmedium (Cambrex™), and then examined for the expression of vWF.

When individual BL-CFCs were transferred to liquid cultures containinggrowth factors supporting the growth of both hematopoietic andendothelial lineages, both non-adherent and adherent cells developed inmore than 60% (15 of 24) BL-CFCs (FIGS. 18d and 18e , Table 2); 65% (16of 24) of them formed hematopoietic colonies including erythroid (FIG.18 i), myeloid (FIGS. 18j and 18k ) and multilineage (FIG. 18l ) afterreplating in semi-solid medium supplemented with a spectrum ofhematopoietic cytokines. Over 95% (23 of 24) of the individual BCsgenerated adherent, stromal-like cells, which formed capillary-vascularstructures on Matrigel (FIG. 18f ) that took up Ac-LDL (FIG. 18g ) andexpressed vWF (FIG. 18h ).

In the second method, individual BCs from both primary and secondaryblast cell colonies were picked and split into two groups; one group wastested for hematopoietic CFU and the other group was tested forendothelial progenitor formation. For primary BCs, over 90% (22 of 24)gave rise to both hematopoetic and endothelial lineages; 100% and 92%developed hematopoetic and endothelial cells, respectively (Table 3).Similarly, seven individual BCs from limiting dilution experiments werealso examined for their potential to differentiate into hematopoieticand endothelial lineages. Five BCs generated both hematopoietic andendothelial progeny (Table 3), showing a lower efficiency than ascompared with BCs from regular experiments (71% vs. 92%), possibly dueto the non-optimal conditions of development. For the 29 secondary BCs,over half (15 of 29) gave rise to both hematopoetic and endotheliallineages, whereas 6 (21%) and 3 (10%) generated only hematopoetic orendothelial cells, respectively (Table 3). Although the primary BCscontained heterogeneous populations, including precursors ofhematopoietic and endothelial cells, the secondary limiting dilutionexperiments clearly demonstrate the existence of hemangioblasts inprimary BCs.

TABLE 3 Hematopoietic and endothelial lineage development fromclonally-derived blast colonies Hematopoietic and endothelial No.Hematopoietic Endothelial lineages colonies lineage (%) lineage (%) (%)Primary BCs* 24 16 (67) 23 (96) 15 (62) Primary BCs** 24  24 (100) 22(92) 22 (92) Primary BCs 7  6 (86)  6 (86)  5 (71) derived from limiteddilution Secondary BCs 29 21 (72) 20 (69) 15 (52) *Individual BCs weretransferred to liquid cultures containing both hematopoietic andendothelial cytokines on fibronectin coated plastic wells. After 1 weekof culture, the non-adherent and adherent cells were removed andexamined for hematopoietic CFU and endothelial cell development.**Individual BCs were transferred to EGM-2 media; half of the cells werecultured on fibronectin coated wells for endothelial lineagedevelopment, and the other half plated directly for hematopoietic CFUassay.

Hematopoietic Progenitor Assay.

For the hematopoietic progenitor assay, half of the cells were mixedwith 1 ml of serum-free hematopoietic colony-forming-unit (CFU) media(H4436, Stem Cell Technologies™) plus 1.5 μg/ml of tPTD-HoxB4 and 0.5%EX-CYTE (Serologicals Proteins Inc.™). Cells may also be mixed withserum-free hematopoetic colony-forming cell assay media containing 1.0%methylcellulose in Iscove's MDM, 1-2% Bovine serum albumin, 0.1 mM2-mercaptoethanol, 10 μg/ml rh-Insulin, 200 μg/ml iron saturated humantransferrin, 20 ng/ml rh-GM-CSF, 20 ng/ml rh-IL-3, 20 ng/ml rh-IL-6, 20ng/ml rh-G-CSF, 3 units/ml rh-Epo, 50 ng/ml rh-SCF) and 1.5 to 5 μg/mlof PTD-HoxB4 fusion protein. The cell mixtures were plated on untreated12-well cell culture plates, and incubated at 37° C. for 10-14 days.

Hematopoietic CFUs were examined under the microscope 10-14 days afterinitial plating. For morphological characterization, singlehematopoietic CFU were picked and washed twice with PBS, cytospun on toa glass slide, stained with Wright-Giemsa dye, and cell morphology wasexamined under a microscope.

As an illustration of the hematopoietic potential of hemangioblasts,hematopoietic CFUs were observed from hemangioblasts that were generatedfrom H1-GFP ES cells, as shown in FIG. 1.

The morphologies of other hematopoietic CFUs that were observed areillustrated in FIGS. 2-6. The CFUs for erythrocytes (CFU-E) werecharacterized by the morphology displayed in FIG. 2. The multipotentCFUs (CFU-GEMM/Mix) were characterized by the morphology displayed inFIGS. 3 and 4. The CFUs for granulocytes (CFU-G) and macrophage (CFU-M)were characterized by the morphology displayed in FIG. 5. The CFUs forgranulocyte/macrophage (CFU-GM) and megakaryocyte macrophage (CFU-Mk)were characterized by the morphology displayed in FIG. 6.

As another illustration of the hematopoietic potential ofhemangioblasts, colonies of erythroid (FIG. 17a ), granulocyte (FIG. 17b), macrophage (FIG. 17c ) and multilineage (FIG. 17d ) hematopoieticcells were also observed when single-cell suspensions were plated inserum-free methylcellulose media containing the spectrum of cytokinesdiscussed above for 10 to 14 days. Wright-Giemsa staining (FIG. 17e-g ),immunostaining (FIG. 17i-k ) and FACS analysis (FIG. 17v-y ) usingantibodies against CD235a (erythocytes), CD13 (myeloid) andCD45(leukocytes) confirmed the identity of their hematopoietic lineages.Most CFUs (>50%) were multilineage with an erythroid core and formedwithin a few days after plating (see FIG. 1 for example).

Erythroid colonies resembled that of primitive erythroid with brilliantred color, Wright-Giemsa staining showed all erythroids were nucleated(FIG. 17e-g ). To further distinguish the developmental stage of theerythroids, CFU colonies were analyzed for the expression patterns ofthe β-cluster globin genes (Lu et al. 2004 Blood (103): 4134-4141). Allthe erythroid and multilineage colonies expressed mainly the embryonicε-globin gene; no β-globin gene message was detected (data not shown),suggesting a primitive yolk-sac-like status.

For immunological characterization, CFU-E, CFU-G, and CFU-Mix cellscytospun onto glass slides were stained with anti-human CD235a, CD13,and CD45 antibodies. For the FACS analysis presented in FIGS. 17 m-p,CFU cells collected from one well were stained with mouse IgG1 isotypecontrol, CD235a, CD13, and CD45 and analyzed by a Coulter flowcytometer. The Wright-Giemsa staining, immunostaining, and FACS analysisconfirmed the identity of their hematopoietic lineages (FIGS. 17e-p ).

For the FACS analysis presented in FIGS. 17v-y , three-color cytometricanalysis was performed using standard procedures on a LSRII flowcytometer (BD Biosciences™). Cells were collected from a well withmultiple types of hematopoietic CFUs and isolated by dilutingmethylcellulose with 5 volumes of IMDM medium. The single cellsuspension was aliquoted and stained with either isotype controls orantigen-specific antibodies. The antibody combinations used were CD235aconjugated to fluorescein-isothiocyanate (FITC), CD45 conjugated toR-Phycoerythrin (R-PE), and CD13 conjugated to-allophycocyanin (APC). Analiquot of cells was also-stained with mouse IgG conjugated to FITC, PE,and APC as isotype controls (BD Bioscience™) Samples were run on a LSRIIflow cytometer and analyzed with FlowJo™ version 6.3.2 software.

Endothelial Progenitor Assay.

For the endothelial progenitor assay, the other half of cells was platedon a fibronectin coated plate (BD Bioscience™) in EGM-2 or EGM-2MVcomplete media (Cambrex™) for 3-7 days. The ability of the isolatedhemangioblast colonies to differentiate into endothelial cells was alsoconfirmed using tube formation on Matrigel, LDL uptake andimmunohistochemistry to detect the presence of endothelial cell surfacemarkers.

Tube Formation on Matrigel.

Matrigel (BD Bioscience™) was added to each well of a 4-well tissueculture plate (0.2 ml) or a 96-well plate (0.05 ml) and allowed tosolidify at 37° C. for 45 to 90 min. After gelation, 0.2-0.3 ml (e.g.,0.1 ml for a 96-well plate) of cell suspension in EGM-2 or EGM-2MV mediacontaining 0.5 to 1.5×10⁵ cells derived from the above culture wasplaced on top of the Matrigel, and incubated at 37° C., 5% CO₂.Formation of capillary-like (tube) structures was checked after 16-24 hrincubation. FIG. 7 depicts a representative photograph of tube-cordformation of hemangioblasts derived from H9 (a) and ACT30 (b) cells;following replating on Matrigel based medium, the hemangioblasts gaverise to adherent cells that formed capillary-vascular like structuresand that also took up Ac-LDL. FIG. 8(a) also depicts a representativephotograph of tube-cord structure of hemangioblasts with endothelialpotential that were derived from H1-GFP cells. FIG. 17q also depicts thecapillary tube-like structures formed on Matrigel after replating theadherent cells derived from hemangioblasts. Such cells were also able totake up AC-LDL (data not shown).

AC-LDL Uptake.

Hemangioblasts grown for 3-7 days on fibronectin coated wells were addedwith 10 μg/ml of Alexa Fluor 647-labeled AC-LDL (Invitrogen™) andincubated for 4-6 hr. The cells were then washed 3 times with 1×PBS andfixed with 4% paraformaldehyde for 30 min. The uptake of AC-LDL wasvisualized under a fluorescent microscope. For example, FIG. 8billustrates the uptake of AC-LDL of hemangioblasts derived from H1-GFPcells. FIGS. 17z and 17 aa also illustrate that incubation withAlexaFluor 594 labeled AC-LDL revealed a punctuate staining patterncharacteristic of endothelial cells.

Immunocytochemistry.

Hemangioblasts grown for 3-7 days on fibronectin coated wells werewashed 3 times with 1×PBS and fixed with 4% paraformaldehyde for 30 min.For the expression of von Willebrand factor (vWF), PECAM-1 (CD31),VE-cadherin, KDR and CD34, cells were permeabilized and then incubatedwith primary anti-human vWF (Dako™ or Chemicon™), PECAM-1 and KDR (CellSignaling Technologies™), VE-cadherin (R&D Systems™), and CD34 (Dako)antibodies respectively overnight at 4° C., then incubated withcorresponding secondary antibodies labeled with Rhodamine or FITC(Jackson Laboratory™) for 30-60 min. The expression of the vWF proteinwas also detected by incubating with a goat anti-mouse IgG-Alexa Fluor647 secondary antibody (Jackson Laboratory™) for 30-60 min. After finalwash, cells were checked under a fluorescent microscope. FIG. 9illustrates the expression of vWF in hemangioblasts that were derivedfrom H1-GFP ES cells. FIG. 17s also illustrates the expression of vWF(arrows) in hemangioblasts-derived endothelial cells. Adherent cells inblood vessel-like structures were positive for PECAM-1 (CD31), KDR andVE-cadherin (FIGS. 17t, 17u, and 17z -17 cc).

Neo-vessel formation was also observed when adherent cells or handpickedBL-CFCs were mixed with Matrigel and implanted in vivo for 4-5 weeks.Histological examination of the Matrigel plugs confirmed the presence ofmicrovessels that were immunoreactive with human specific nuclei and vWFantibodies. See FIGS. 10 and 11.

Example 3 Method of Producing and Purifying an Exemplary HOXB4 Protein

An exemplary HOXB4 protein is made and purified. This is a TAT-HA-HOXB4fusion protein.

A pTAT-HA-HoxB4 expression vector was generated by cloning a PCRfragment (sense primer 5′-TAC CTA CCC ATG GAC CAC TCG CCC-3′ (SEQ ID NO:16) and antisense primer 5′-TCG TGG CTC CCG AAT TCG GGG GCA-3′ (SEQ IDNO: 17) encompassing the HoxB4 open reading frame with and withoutN-terminal 32 amino acids into the NcoI and EcoRI sites of pTAT-HAexpression vector (a gift from Dr. SF. Dowdy, University of CaliforniaSan Diego, La Jolla, Calif.), which contains an N-terminal TAT PTD. Thegenerated pTAT-HA-HoxB4 plasmid was confirmed by sequence analysis andtransformed into BL21(DE3) pLysS bacteria (Invitrogene™)

Bacterial cells growing at log phase were induced with 1 mM IPTG at 30 Cfor 4 hours and collected by centrifugation. Since the 6×His-fusedrecombinant TAT-HoxB4 protein was found to be sequestered into inclusionbodies by the host bacteria, the cells were disrupted by sonication indenaturation solution (6 M guanidinium, 20 mM NaPO₄, and 0.5 M NaCl, pH7.8) and the 6×His-fused TAT-HoxB4 recombinant proteins were then boundto nickel resins (ProBond resin, Invitrogen™).

After several washings, the TAT-HoxB4 fusion proteins were eluted in 20mM NaPO₄, pH 4.0, 0.5 M NaCl, 8 M urea plus 10 mM imidazole. TheTAT-HoxB4 fusion proteins were then desalted on a Sephadex G-25 columninto IMDM medium, aliquoted and stored at −80° C. immediately.

The purity and concentration of the TAT-HoxB4 fusion proteins weredetermined by SDS-PAGE gel electrophoresis and visualized with Coomassieblue staining. The purified TAT-HA-HoxB4 recombinant protein runs as a≈37 KD protein. The concentration of the purified TAT-HA-HoxB4 proteinwas estimated by comparison with a BSA protein standard in the same gel.

Based on computer modeling, Ho et al. (2001 Cancer Res 61: 474-477)demonstrated that a modified PTD possesses significantly enhancedprotein transduction potential compared with the native TAT PTD, both invitro and in vivo. To produce the modified PTD-HA-HoxB4 fusion protein,sense 5′-CGA TGG GGA TCC GGC

GGT GGA TCC ACC ATG-3′ (SEQ ID NO: 18) and antisense 5′-CAT GGT GGA TCCACC

GCC GGA TCC CCA TCG-3′ (SEQ ID NO: 19) oligos were digested with BamHIand purified using a kit (Qiagen™). Then TAT fragment in pTAT-HA-HoxB4plasmid was replaced with the modified PTD fragment, and triplicated PTDinserts were selected based on restriction fragment size and confirmedby DNA sequence analysis. This plasmid is referred to as ptPTD-HA-HoxB4.pTAT-HA-HoxB4 and ptPTD-HA-HoxB4 plasmids were transformed intoBL21(DE3) pLysS bacteria (Invitrogen™), and HoxB4 fusion proteinexpression was induced by the addition of 1 mM IPTG at 30° C. for 4 h.The 6×His-fused recombinant TAT-HoxB4 and tPTD-HoxB4 proteins weresequestered into inclusion bodies by the host bacteria, so the cellswere disrupted by sonication in denaturation solution (6 M guanidinium,20 mM NaPO₄, and 0.5 M NaCl, pH 7.8) and the 6×His-fused TAT-HoxB4 andtPTD-HoxB4 recombinant proteins were then bound to nickel resins(ProBond resin, Invitrogen™) After several washings, the TAT-HoxB4 andtPTD-HoxB4 fusion proteins were eluted in 20 mM NaPO4, pH 4.0, 0.5 MNaCl, 8 M urea plus 10 mM imidazole. The TAT-HoxB4 and tPTD-HoxB4 fusionproteins were then desalted in Sephadex G-25 columns into IMDM medium,and aliquoted and stored at −80° C. immediately. The purity andconcentration of the TAT-HoxB4 and tPTD-HoxB4 fusion proteins weredetermined by SDS-PAGE gel electrophoresis and visualized with Coomassieblue staining. The purified TAT-HoxB4 and tPTD-HoxB4 recombinantproteins ran as ≈38 KD proteins. The concentrations of the purifiedTAT-HoxB4 and tPTD-HoxB4 proteins were estimated by comparison with aBSA protein standard in the same gel. For stability assays, TAT-HoxB4and tPTDHoxB4 proteins were added to IMDM medium with 5% FBS or StemlineII medium with live hESCs in Ultra low 24-well plates and incubated at37° C. Aliquots of the medium were removed at different times andsubjected for SDS-PAGE gel electrophoresis, and visualized withCoomassie blue staining.

Beslu et al. (2002 Blood 100: 22a) have reported that the first 31 aminoacids of the N-terminus of HoxB4 are dispensable for its function, andthat the removal of the N-terminal 33 amino acids generates a morestable protein. The results confirmed that the full length TAT-HoxB4protein was unstable, forming a ≈30 KD protein after several thawingcycles, whereas the N-terminus-deleted TAT-HoxB4 and tPTD-HoxB4 proteinsretained their integrity after repeated thawing and overnight incubationat 37° C. (FIG. 19C). As shown in FIG. 19A, tPTD-HoxB4 and TATHoxB4 wererelatively pure proteins after multiple column chromatography underdenaturing conditions and desalting. The purified tPTD-HoxB4 protein ranas a single ≈38 KD band under native SDS-PAGE, with a maximum solubilityin PBS or IMDM medium of 250 to 300 μg/ml as estimated by comparisonwith BSA protein standards. Similar results were obtained from theTAT-HoxB4 fusion protein.

Krosl et al. (2003 Nat Medicine 9: 1428-1432) have observed thatTAT-HoxB4 protein is very unstable in environments containing FBS and ithas to be refreshed every second hour in order to retain biologicalfunction. The results presented here confirmed that tPTD-HoxB4 waslabile in medium containing 5% FBS, with a half life less than one hour(FIG. 19B); pretreatment of FBS at 70° C. for 30 minutes eliminated mostof the enzymatic activity. To further examine its stability, tPTD-HoxB4protein was added to serum free Stemline medium and cultured with hESCsat 37° C. As shown in FIG. 19C, a substantial fraction of tPTD-HoxB4protein could be detected, even after 48 h of culture with hESCs.

Example 4 Matrigel Plugs Transplanted into SCID Mice Give Rise toEndothelial Cells

Hemangioblast-derived endothelial cells or pure hemangioblasts (1×10⁶cells) derived from H1-GFP human ES cells were purified and resuspendedin 700 μl of Matrigel (BD Biosciences™). These cells were injectedsubcutaneously in the dorsal region of 4-week-old SCID mice (JacksonLaboratory™). Five weeks after injection, the Matrigel plugs wereremoved from the animals and frozen sections were prepared from theplugs. Cross sections of the Matrigel plugs were fixed, and stained bystandard hematoxylin and eosin (H&E) staining, as well asimmunohistochemistry using an anti-human specific nuclei antibody(MAB1281, Chemicon™) and human specific anti-vWF antibody, followed byfluorescent dye labeled corresponding secondary antibodies (goatanti-mouse IgG-Texas Red secondary antibody for MAB1281). FIG. 10demonstrates vessels in cross sections of Matrigel plugs with H&Estaining; and FIG. 11 demonstrates that the vessels in cross sections ofMatrigel plugs are cells derived from human hemangioblasts, which arepositive for human specific nuclei antibody.

Example 5 In Vivo Ischemia/Reperfusion Studies of the Eye

Two techniques, intravitreal injection and adoptive transfer, were usedto directly examine the contribution of the hES-derived hemangioblaststo the in vivo repair process. Ischemia/reperfusion (I/R) injury wasinduced by elevation of the intraocular pressure. This model of I/Rinjury results in damage to the retinal endothelium includingvaso-obliteration and generation of acellular capillaries. Seven daysfollowing retinal I/R injury, the mice were injected either systemicallyvia the retro-orbital sinus (n=13) or intraviterally (n=4) withfluorescently labeled hemangioblast (also referred to as “hES-BC”) cellscollected from day 6 hES-BCs.

One day following injection, the mice were euthanized and the retinasremoved and labeled with rhodamine-conjugated Ricinus communisagglutinin I. This agglutinin binds to glycoproteins expressedspecifically by endothelial cells and thus is used to fluorescentlylabel the exterior surfaces of blood vessels.

Confocal microscopy demonstrated green fluorescent labeling forhemangioblast (hES-BC) derived endothelial cells, which represented33.5±10% of the retinal vasculature in the injured eye. No greenfluorescence was observed in the control eye (FIGS. 20a and 20b ,respectively), demonstrating that the hemangioblast (hES-BC) cells homedto acellular regions where they assimilated into injured regions only,resulting in reendothelialization of non-perfused acellular capillarieswithin the injured retina (FIGS. 21a and 21b ). This repair process wasobserved in all (n=17) animals in a uniform manner.

A second set of animals with I/R injury (n=6) were handled as describedabove, and were then, prior to sacrifice, perfusion-fixed with 3-5 ml ofTRITC-conjugated dextran in order to visualize vascular lumens ofvessels and to conclusively demonstrate that vessels repaired by thesecells were patent and thus functional. Red staining depicted patentvessels, green staining demonstrated the hemangioblast (hES-BC) derivedendothelial cells, and yellow staining showed where hemangioblast(hES-BC) cells have generated a patent vasculature. FIG. 21d shows alarge vessel with yellow (red and green, appearing as light gray)fluorescence two days after hES-BC cell injection, indicating that thecells had incorporated into the vascular wall and that the vessel wasperfused. Particularly striking in these animals was the large number ofmicrovessels that were observed to be only green, which appeared torepresent new collateral compensatory neovasculature that had not yetmatured enough to develop patent lumens, and therefore remainednonperfused with TRITC-dextran. FIG. 20c shows the uninjured control eyeof the same animal and clearly demonstrates that BC cells were not inany way associated with vasculature that has had no injury. In retinalflatmounts from mice sacrificed 7 days following hES-BC cell injection,the number of green tubes (non-lumenized, non-perfused vessels) was lesscompared to mice sacrificed on day 2. There were more yellow vessels(appearing as light gray or white) representing hES-BC cell derivedvessels (green) perfused with TRITC-dextran (red). These representedfully functional vessels and demonstrated that hemangioblast (hES-BC)cells had incorporated into vessels of injured eyes which resulted inmore areas with perfused microvessels (FIG. 20e ).

Fluorescent immunocytochemistry colocalizes hemangioblast (hES-BC)cell-derived endothelial cells to existing injured vasculature in crosssections of mouse eyes that underwent I/R injury, and a representativecross section of a vessel in the ganglion cell layer in a retina from aninjured eye is shown (FIG. 20f ). Colocalization of human nuclearantigen staining with anti-CD31 staining of the vessel suggests thatsome endothelial cells in the vasculature were derived fromhemangioblast (hES-BC) cells. FIG. 20f shows a high magnification viewof a vascular lumen in the ganglion cell layer adjacent to the innerlimiting membrane. The lumen is surrounded by endothelial cells (FIG.20f , arrowhead, CD31) and also by mature endothelial cell(s) derivedfrom hemangioblast (hES-BC) cells (FIG. 20f , arrow, human nuclearantigen).

Methods.

For the in vivo ischemia/reperfusion studies, C57BL6/J mice (JacksonLaboratory) were age 7 to 10 weeks of age at the beginning of the study.The ischemia/reperfusion injury was induced by elevation of theintraocular pressure (IOP). Mice were kept under inhalation anesthesia(Isoflurane vapor) during induction of ischemia. The anterior chamber ofthe eye was cannulated with a 30-gauge needle attached to an infusionline of saline and the eye was subjected 2 h of hydrostatic pressure(80-90 mmHg measured by Tono Pen; Medtronic Solan, Jacksonville, Fla.)on the anterior chamber. This resulted in retinal ischemia as confirmedby whitening of the iris and loss of the red reflux. After 120 minutesthe needle was withdrawn and the IOP was normalized, resulting inreperfusion injury. The contralateral eye served as a control.

Seven days following retinal ischemia reperfusion injury, the mice wereinjected either systemically via retro-orbital sinus (n=13) or injectedintravitreally (n=4) with fluorescently labeled hemangioblasts collectedfrom day 6 hES-BCs. Fluorescent vital labeling of hemangioblasts wasaccomplished using the dye PKH-67 (Sigma-Aldrich™) according tomanufacturer's guidelines. For systemic injection each mouse received4×10⁵ labeled hemangioblasts in 100 μl, while for intravitreal injectioneach mouse received 5×10⁴ hemangioblasts in 2 μl. The contralateralcontrol eye of the intravitreous injection group was injected with anequivalent volume of sterile isotonic saline. One day later the micewere euthanized and the eyes removed and fixed in 4% paraformaldehydefor 1 h. After washing, the eyes were dissected by a circumferentiallimbic incision to remove the cornea and lens, followed by the vitreoushumor. The intact neural retina was next removed by gently detaching itfrom the underlying choroid. The intact retina was placed inpermeabilization buffer. The retinas were isolated and incubatedovernight at 4° C. in 1:1000 Rhodamine-conjugated R. communis agglutininI (Vector Laboratories) in 10 mM HEPES, 150 mM NaCl and 0.1% Tween 20(pH 7.5). After 24 h, the retinas were washed in 10 mM HEPES and 150 mMNaCl at for 24 h at 4° C. and then mounted on coverslips for imagingusing an MRC-1024 Confocal Laser Scanning Microscope (BioRad) at theOptical Microscopy Facility at the University of Florida (Gainesville).Alternatively, a Zeiss laser scanning confocal microscope was used toimage the retinas.

For microscopy using the Zeiss laser scanning microscope, the retinaswere placed on glass coverslips and their curvature was flattened by 4or 5 radial incisions extending from the ciliary margin to within 1 mmof the optic disc. Simultaneous red and green fluorescence digital imagecaptures of the mounted retinas were then made with a Zeiss laserscanning confocal microscope using either a 10× or 20× objective. Thez-section depth was kept constant at 2 μm, and the entire retinalvasculature through the thickness of the neural retina (which includesthe superficial, mid, and deep vascular plexi) was scanned, resulting intypically 25-35 z-section images per fluorescent channel. Image captureswere made from random locations in the mid-periphery of the retinas asthese areas are where the most vascular damage is typically observed inthese models. The 3-dimensional z-stacks were then flattened usingImageJ software (ImageJ 1.37c, Wayne Rasband, National Institutes ofHealth, USA, http://rsb.info.nih.gov/ij/index.html) so that the threevascular plexi are visible in a single 2-dimensional plane.

A second set of mice (n=6) that were also subjected to I/R injury in theright eye received approximately 2×10⁵ PKH-67-labeled hES-BCs orhemangioblasts in 100 μl administered by left retro-orbital sinusinjection. Mice were euthanized at 2 days and 7 days (n=3 each) postinjury and perfused with 3-5 ml TRITC-conjugated dextran(Sigma-Aldrich®, St. Louis, Mo., 5 mg/ml) in 4% bufferedparaformaldehyde via left ventricular puncture. Eyes were then removed,dissected, and the retinas mounted flat for digital image capture byconfocal microscopy as described earlier. The contralateral (uninjured)eye served as the control. This perfusion fixation method allows thevisualization of patent vessels, as only functional vessels can beperfused.

Example 6 In Vivo Repair in a Diabetes Model

In vivo repair was also studied in spontaneously diabetic obeseBBZDR/Wor rats with Type II diabetes of greater than 3 months. Theserats develop many characteristics of pre-proliferative diabeticretinopathy including acellular capillaries and endothelial dysfunction,pericyte loss, and blood retinal barrier breakdown (Shi et al. 1998Blood (92): 362-367; Asahara et al. 1997 Science (275): 964-967; Kalkaet al. 2000 Circ. Res. (86): 1198-1202; Murohara et al. 2000 J. Clin.Invest. (105): 1527-1536; Urbich et al. 2004 Trends Cardiovasc. Med.(14): 318-322).

Male obese type 2 diabetic BBZDR/Wor rats (Biomedical Research Models,Worcester, Mass.) with duration of diabetes of at least 3 months, alongwith lean age- and sex-matched controls, were used to examine theability of BCs to participate in reendothelialization of damagedcapillaries. Rats were immune suppressed by intramuscular injection ofcyclosporine (2 mg/Kg/day) beginning one day prior to administering thecells, and continuing for the duration of the study. hES-EBc werepelleted by centrifugation and resuspended in sterile saline at aconcentration of 3×10⁴/μl; 5 μl of that suspension was injected intoeach eye of each of six diabetic and control rats. The animals wereeuthanized 2 days (n=3 diabetic, n=3 control) and 7 days (n=3 diabetic,n=3 control) after administering the hES-BCs. Four of the six eyes fromeach treatment group were processed and retinal flatmounts were preparedas described for the mouse I/R study using rhodamine-conjugated R.communis to visualize vessels. The rat retinas were additionally reactedwith monoclonal anti-GFP (Chemicon™, Temecula, Calif.; 1:250 in PBS)followed by FITC-conjugated goat anti-mouse IgG (Abcam™, Cambridge,Mass.; 1:200 in PBS) to visualize the GFP-expressing BCs. Digital imagecaptures were performed by confocal microscopy as described for themouse I/R study.

The remaining two eyes from each treatment group were fixed, dehydratedin 2.5M sucrose, and then embedded in OCT medium for cryosectioning. Atleast 50 sections (10 μm thickness, every 10th section kept) werecollected and reacted (with appropriate washes between incubations) withmonoclonal rat anti-CD31 (Abcam™, 1:100 in PBS), rabbit antihuman vWF(Sigma-Aldrich™, 1:200 in PBS), and 1:50 biotinylated anti-human nuclearantigen, followed by FITC-conjugated anti-rat IgG (Sigma-Aldrich®, 1:320in PBS) and AMCA-conjugated goat anti-rabbit IgG (Vector Laboratories™,Burlingame, Vt., 1:75 in PBS), and finally Texas red-conjugatedstreptavidin (Vector Laboratories, 1:500 in PBS). The sections were thenmounted with Vectashield antifade medium (Vector Laboratories™) anddigital image captures were made with a Zeiss Axioplan 2 epifluorescencemicroscope coupled to a Spot CCD camera.

As in the I/R mouse model, intravitreally administered hES-BC cells(hemangioblasts) incorporated extensively into areas with both largerand smaller (FIGS. 21a and 21b ) vasculature. FIG. 20b also reveals alarge vessel that is nearly all green and narrows very rapidly (lightgray vessel on the top right of FIG. 21b ). These “pinched-off” vesselsare characteristic of pre-proliferative diabetic retinopathy, wheremicrothrombi result in vessel degeneration and downstream ischemia.Small vessels that continue from and branch extensively from thispinched larger vessel show a high degree of incorporation of green BCcells (shown as light gray in FIG. 21). By contrast, no green hES-BCcells colocalized with resident vessels in eyes from the non-diabeticcontrol animal. Eyes from the non-diabetic control animal confirm thatthe BC cells do not incorporate into the uninjured vasculature butrather remain as sheets atop the retina after intravitrealadministration of hES-BC cells (FIG. 21c , light gray area).

Immunohistochemical analysis showed colocalized staining with CD31 andhuman nuclear antigen in cells lining vessel lumens in the ganglion celllayer of the diabetic rat retinas (FIGS. 21e and 21f ), immediatelyposterior to the internal limiting membrane that separates the neuralretina from the vitreous. This anatomical location is the site of thesuperficial retinal vascular plexus and is the typical location ofvascular pathology in diabetes. This precise localization and robustincorporation clearly demonstrates that hemangioblasts participate inrepair of vessels that are involved in diabetic retinopathy. Mostsections showed vessels with clearly visible lumens whose peripherieswere lined with cells staining for both endothelial (CD31) and humannuclear antigen markers (FIGS. 21e and 21f , arrows), whereas there wasno evidence of hemangioblast (hES-BC) cell incorporation in thenon-diabetic control rat eyes that were also injected with BC cells(FIG. 21d , arrows).

Example 7 In Vivo Repair in a Murine Hind Limb Ischemic Model

The ability of BC cells to generate vascular endothelial cells was alsoexamined in a murine hind limb ischemic model. The experiments wereperformed on 8- to 12-week-old (20-30 g) NOD-SCID β2 mice (JacksonLaboratory). Ischemia of the right hind limb was induced by femoralartery ligation surgery, and hemangioblast (hES-BC) cells (6×10⁵ hES-BCcells) or cell free medium were injected into the area of peri-ischemicmuscle immediately following the surgery.

To demonstrate physiological functions of injected hemangioblast(hES-BC) cells, right ischemic hind limb blood flow was monitored for 4weeks and compared with blood flow of the left normal hind limb. Animmunofluorescent technique was used to detect human specific vWF (R andD System™, MN) and to identify blood vessel endothelial cells fromengrafted hemangioblast (hES-BC). A secondary antibody conjugated withAlexa Fluor 594 was used. For blood flow analysis, laser Dopplerblood-flow imaging was used to asses the blood flow in mice before (day0) and after (day 3 to 30) femoral artery ligation, and blood flow rateis calculated as the ratio of flow in the ischemic limb to that in thenon-ischemic limb.

As shown in FIGS. 22f and 22g , hemangioblast (hES-BC) cellssignificantly enhanced the restoration of blood flow rate in ischemiclimbs as compared to medium control (p<0.0001). Improvement persistedfor four weeks until near normal flow rates were achieved.

Four weeks after injection of hES-blast colony cells into theperi-ischemic muscle, the animals were sacrificed and immunostained forhuman specific vWF. Intra-muscular areas were identified containingpositive staining of human specific vWF cells showing vascularorganization (FIG. 22 d-e). Control tissue from infarcted muscleinjected with cell free medium showed no human vWF staining (FIG. 22c ).

Example 8 In Vivo Repair in a Murine Myocardial Infarct Model

In a series of experiments in the murine myocardial infarct (MI) model,myocardial infarction was induced in 8 to 12 week old (˜20-30 gram)NOD/SICD β2 mice (Jackson Laboratory™) by ligation of the left coronaryartery as described previously (Yang et al. 2002 J. Appl Physiol (93):1140-1151). Fifteen minutes after MI induction, 3×10⁵ GFP-hemangioblast(hES-BC) cells derived from H1-GFP hES cells or cell free medium weretransplanted into the ischemic and peri-ischemic myocardium. Theexperimental protocol was approved by the Animal Care Committee ofMemorial Sloan-Kettering Cancer Center. Thirty days post hemangioblast(hES-BC) cell injection, 71% (12/17) of the animals injected withhemangioblast (hES-BC) cells survived as compared to 42% (8/19) animalsinjected with medium control (FIG. 22h , P<0.002).

Animals were sacrificed four weeks after injection of hemangioblast(hES-BC) cells into ischemic and peri-ischemic myocardium and the heartswere quickly removed and washed in PBS. The hearts were embedded intissue freezing medium (Fisher Scientific™, NJ). Frozen tissue wassectioned to 10-μm slides.

Infarcted tissue recovered for immunostaining demonstrated that areas ofregenerating tissue contained considerable numbers of endothelial cellsstaining specifically for human vWF. Confocal microscopy confirmed theincorporation of human specific vWF-positive endothelial cells into thelumen of microvessels in the infarcted tissue (FIG. 22i ). These cellswere closely associated but had not yet formed highly organized vasculartissue (FIG. 22b ). No human vWF positive cells were detectable ininfarcted heart tissue from control mice (FIG. 22a ).

The transplanted hemangioblast (hES-BC) cells also gave rise to cardialmyocytes. To identify regenerated myocytes from engrafted hemangioblast(hES-BC) cells, a double immunofluorescent staining technique was usedto detect GFP that expressed only in human cells derived from H1-GFP hEScells (Santa Cruz Biotechnology Inc.™, CA) and cTnI, a cardiomyocytemarker (Santa Cruz Biotechnology Inc.™, CA). A secondary antibodyconjugated with Alexa Fluor 488 for GFP or Alexa Fluor 594 for TnI wasused. Images were taken under fluorescent microscopy. N=3. FIG. 23 showsimmunostaining of GFP (brightest or lightest stained areas) and cTnI(medium gray areas) on MI mice; cells stained positive for both GFP andcTnI are cardiomyocytes derived from injected hES=BC cells (FIG. 23,magnification 200×). The arrows indicate double positive staining cellsderived from injected hES-BC cells.

The results from Examples 7 and 8 demonstrate that hemangioblast cellsreduce mortality after myocardial infarction and restore blood flow tonear normal level in ischemic hind limbs.

Example 9 Hemangioblasts or hES-BC Cells can Give Rise to Smooth MuscleCells In Vitro

The hemangioblasts, or hES-BC cells, of the present invention can alsodifferentiate into smooth muscle cells, and thus, in certainembodiments, may be pluripotent.

To examine gene expression in the hemangioblast (hES-BC) cells, cellswere handpicked under dissection microscope at day 6 and total RNA wasisolated. Using an RNAeasy Micro Kit (Qiagen™), the RNA was subjected tofirst strand cDNA synthesis with SMART II and CDS primers (Clontech™),using Superscript III reverse transcriptase (Invitrogen™), and cDNApools were constructed using the SMART cDNA synthesis kit (Clontech™).Smooth muscle gene expression pattern was analyzed using primersspecific for smooth muscle calponin (CNN1), SM22, smooth muscle actin(α-SMA) and GAPDH (quality control) by PCR. Total RNA from human aortasmooth muscle cells (AoSM) was used as a positive control, and mousefibroblast 3T3 total RNA was used as a negative control. PCR productswere separated on a 1% agarose gel and exposed by ethidium bromidefluorescence.

FIG. 24 shows that hemangioblast (hES-BC) cells express smooth musclespecific genes CNN1, α-SMA and SM22.

To derive smooth muscle cells from the hemangioblasts of the presentinvention, purified hemangioblast (hES-BC) cells were plated onfibronectin-coated culture slides (BD Bioscience™) in Smooth MuscleMedium (Lonza™) and differentiation was induced for 2-9 days. Cells werethen fixed with 4% paraformaldehyde for 15 min, washed with 1×PBS andpermeabilized with 0.4% Triton X100. For detecting the expression ofsmooth muscle proteins, the permeabilized cells were incubated withprimary antibodies against calponin (CNN1) and α-SMA (Dako) at 4° C.overnight, then followed by Rhodamine labeled secondary antibodies andexamined under fluorescent microscope.

The results presented in FIG. 24 clearly demonstrate that somehemangioblast (hES-BC) cells give rise to CNN1 and α-SMA positive smoothmuscle cells after in vitro differentiation under the above conditions.

Example 10 Induction of Immunological Tolerance in Transplant Recipientsin a Mouse Model System

Human hemangioblast cells generated and expanded according to themethods of the present invention may be used to induce donor-specifictolerance in transplant recipients. Hemangioblasts or derivativehematopoietic stem cells can engraft in unconditioned recipients whenthe cells are given in large numbers. The ability of hemangioblasts toengraft and produce chimerism may be tested in the immunocompromisedNOD/SCID-Tg mouse model system in which mice have been reconstitutedwith human immune cells. Immunodeficient NOD/SCID-Tg mice can be treatedwith whole body irradiation and injected with human donor hemangioblastson the same day. Human fetal thymus and fetal liver fragments areimplanted under the kidney capsule of mice to achieve humanlymphopoiesis and reconstitution of the human immune system. Theimplanted human thymus and liver fragments are mismatched with respectto the human donor hemangioblasts. The mice can then be tested fortolerance to grafts matched to the human hemangioblasts as compared totolerance to third party, non-matched grafts.

In order to optimize engraftment, thymic space may be induced by theadministration of thymic irradiation. In the mouse model, recipient micecan receive anti-T cell mAbs such as anti-CD4 and anti-CD8 mAbs, 7 Gythymic irradiation on day 0, and human hemangioblasts on days 0 through4.

To evaluate tolerance, mixed lympyhocyte reactions and cell mediatedlympholysis studies may be

Additionally, human hemangioblasts can be substituted for the humanfetal liver fragments in the method described above in order to test theability of the hemangioblasts to induce chimerism in the hu-SCID mouseor similar model system.

Example 11 Induction of Immunological Tolerance in Transplant Recipients

In humans, tolerance may be achieved using the large numbers of humanhemangioblasts generated and expanded or expanded by the methods of thepresent invention.

Peripheral chimerism may be achieved through the large numbers ofhemangioblasts without the need for whole body irradiation. However, toachieve central deletional tolerance, it may be optimal to create spacein the thymus in order to allow high levels of intrathymic chimerism todevelop. Space in the thymus can be achieved by specific irradiation orby the use of multiple administrations of anti-T cell antibodies or withdrugs that deplete the thymus.

The following procedure is designed to lengthen the time an implantedorgan, tissue, or cell survives in a patient (graft survival) and todecrease the level of immunosuppression required in transplantationprocedures. The organ can be any organ, e.g., a liver, a kidney, apancreas, or a heart. Tissue can be any type of tissue, such as skin,bone, corneas, tendons, ligaments, heart valves, etc. Cells or celltherapies include, but are not limited to, hematopoietic cells (such as,for example, mesenchymal stem cells as a treatment for ischemia or othercells for the treatment of hematologic disorders), pancreatic cells suchas insulin-secreting pancreatic beta-cells for the treatment of diabetesmellitus, retinal pigment epithelium cells for the treatment of maculardegeneration, and cell-based therapies for the treatment of neurologicaldisorders.

The method may include one or more of the following steps: inactivationof recipient T cells or costimulatory blockade; inactivation ofrecipient NK cells; transplantation of tolerance-inducing cells, e.g.,human hemangioblasts; optionally, the implantation of donor stromaltissue or administration of human cytokines; and the administration ofthymic irradiation. The combination of a sufficiently large number ofdonor human hemangioblasts in combination with thymic irradiation and/orT cell costimulatory blockade significantly reduces or eliminates theneed for whole body irradiation. The method may include any or all ofthese steps, and the steps may be carried out in the following sequence.

First, a preparation of horse anti-human thymocyte globulin (ATG) orother depleting anti T cell depleting agent is intravenously injectedinto the recipient. The antibody preparation eliminates mature T cells.If not eliminated, mature T cells could promote rejection of both thehuman hemangioblast cells or hematopoietic stem cells derived therefrom,and, after sensitization, the graft itself. The ATG preparation alsoeliminates natural killer (NK) cells. NK cells probably have no effecton the implanted organ, but may act immediately to reject the newlyintroduced human hemangioblast cells.

The presence of donor antigen in the recipient thymus during the timewhen recipient T cells are regenerating post-transplant is critical fortolerizing recipient T cells. If donor human hemangioblasts are not ableto become established in the recipient thymus and induce tolerancebefore recipient T cells regenerate, repeated doses of anti-recipient Tcell antibodies may be necessary throughout the non-myeloablativeregimen. Continuous depletion of recipient T cells may be required forseveral weeks.

The second step in the non-myeloablative procedure may be to supplyspecific growth factors or cytokines, to promote engraftment of donorhuman hemangioblast or stem cells.

Human hemangioblast cells of the donor (or that are matched to thedonor) may then be injected into the recipient. Donor cells home toappropriate sites of the recipient and grow contiguously with remainingrecipient's cells and proliferate, forming a chimericlymphohematopoietic population. By this process, newly forming B cells(and the antibodies they produce) are exposed to donor antigens, so thatthe transplant will be recognized as self.

Tolerance to the donor is also observed at the T cell level inrecipients in which human hemangioblast or derived hematopoietic stemcells engraftment has been achieved. When a matched organ graft isplaced in such a recipient several months after hematopoietic or bonemarrow chimerism has been induced, the graft should be accepted by boththe humoral and the cellular arms of the immune system. This approachhas the added advantage of permitting organ transplantation to beperformed sufficiently long after transplant of donor humanhemangioblast cells such that the normal health and immunocompetence ofthe recipient patient will have been restored at the time of organtransplantation.

Many of the methods to create hematopoietic space utilize whole bodyirradiation, thereby promoting engraftment. The need for irradiation maybe substantially reduced or eliminated by the administration of largenumbers of donor hemangioblast cells. Administration of donor humanhemangioblasts may be combined with a treatment, e.g., thymicirradiation, which induces thymic space, or T cell costimulatoryblockade.

Finally, T cells, particularly, thymic or lymph node T cells, may befurther suppressed by administering to the recipient a short course ofan immunosuppressive agent, e.g., cyclosporine or similar agent

To evaluate tolerance, mixed lympyhocyte reactions and cell mediatedlympholysis studies may be performed in recipients.

While any of these procedures may aid the survival of an implantedorgan, tissue, or cell, best results may be achieved when some or all ofthe steps are used in combination.

Example 12 Human RBC Transfusion

In order to confirm the viability and functionality of red blood cells(RBCs) produced by the methods of the invention, transfusions usinghuman RBCs will be performed in NOD-scid mice. Mice will besplenectomized under Nembutal anesthesia one week prior to transfusion.Recipients will be bled immediately prior to transfusion to drop thehematocrit to 25%. Within one hour after bleeding, recipients will betransfused via i.v. injection with 6×10⁹ human RBVs in 0.5 mL PBS. Cellsfrom the initial transfusion will be labeled with carboxyfluoresceindiacetate (CFSE) for fluorescent monitoring purposes. Transfusions willbe repeated on day two and every four days thereafter. On day 1post-transfusion and every four days thereafter for up to 4 weeks,recipient mice will be monitored by collecting 20 μL of blood from atail nick with a heparinized capillary tube. The percentage of RBC andhuman RBC will be determined by microscopy and flow cytometry withFITC-anti-Fy6 antibody. The half-life of transplanted cells will becalculated. Expression of hemoglobin F will be determined to verifyoxygen transport capacity of RBCs. It is expected that the RBCs willexpress hemoglobin F and have a half-life comparable to normally derivedRBCs. It is therefore expected that the RBCs will be functional.

The present disclosure demonstrates that hemangioblasts, or human ES-BCcells, can be reliably derived and expanded under well-defined andreproducible conditions-representing an inexhaustible source of cellsfor patients with compromised vasculature. The concentration of thesecells would not be limited by availability, but rather could be titratedto the precise clinical requirement of the individual. Repeated infusionof the identical cell population over the lifetime of the patient wouldalso be possible if deemed necessary by the physician. Furthermore, theability to create banks of matching or reduced-complexity HLA hES linescould potentially reduce or eliminate the need for immunosuppressivedrugs and/or immunomodulatory protocols altogether.

This disclosure also demonstrates for the first time that hemangioblastsderived from embryonic stem cells can be used to achieve vascular repairin four different animal models. The formation of new blood vessels wasrapid and robust, thus indicating that hES-derived hemangioblasts haverobust reparative potential in vivo. These results also indicate thathemangioblasts may be used to restore vascularization and function inpatients with vascular disease. Adoptive transfer of endothelialprecursor cells such as hemangioblasts may therefore be useful inrestoring blood flow and increasing capillary density, decreasing limbloss and facilitating recovery from myocardial injury.

This disclosure further provides methods for generating differentiatedcell types for use in transfusion. For example, this disclosure providesmethods for generating red blood cells for use in transfusion. Incertain embodiments, the red blood cells express hemoglobin F.

All experiments were performed in accordance with the protocol approvedby the Animal Care and Use Committee of The University of Florida andthe tenets of the ARVO Statement for the Use of Animals in Ophthalmicand Vision Research.

SEQUENCE LISTING(Human HOXB4 amino acid sequence-GenbankA ccession No: GI:13273315)SEQ ID NO: 1    1mamssflinsnyvdpkfppceeysqsdylpsdhspgyyagggrressfqpeagfgrraac   61tvqryaacrdpgpppppppppppppppglsprapapppagallpepgqrceavssspppp  121pcaqnplhpspshsackepvvypwmrkvhystvnpnyaggepkrsrtaytrqqvleleke  181fhynryltrrrrveiahalclserqikiwfqnrrmkwkkdhklpntkirsggaagsaggp  241pgrpnggpral (Human HOXB4 DNA sequence-Genbank Accession No: GI:85376187)SEQ ID NO: 2    1GGAAAACGAGTCAGGGGTCGGAATAAATTTTAGTATATTTTGTGGGCAATTCCCAGAAAT   61TAATGGCTATGAGTTCTTTTTTGATCAACTCAAACTATGTCGACCCCAAGTTCCCTCCAT  121GCGAGGAATATTCACAGAGCGATTACCTACCCAGCGACCACTCGCCCGGGTACTACGCCG  181GCGGCCAGAGGCGAGAGAGCAGCTTCCAGCCGGAGGCGGGCTTCGGGCGGCGCGCGGCGT  241GCACCGTGCAGCGCTACGCGGCCTGCCGGGACCCTGGGCCCCCGCCGCCTCCGCCACCAC  301CCCCGCCGCCCCCGCCACCGCCCGGTCTGTCCCCTCGGGCTCCTGCGCCGCCACCCGCCG  361GGGCCCTCCTCCCGGAGCCCGGCCAGCGCTGCGAGGCGGTCAGCAGCAGCCCCCCGCCGC  421CTCCCTGCGCCCAGAACCCCCTGCACCCCAGCCCGTCCCACTCCGCGTGCAAAGAGCCCG  481TCGTCTACCCCTGGATGCGCAAAGTTCACGTGAGCACGGTAAACCCCAATTACGCCGGCG  541GGGAGCCCAAGCGCTCTCGGACCGCCTACACGCGCCAGCAGGTCTTGGAGCTGGAGAAGG  601AATTTCACTACAACCGCTACCTGACACGGCGCCGGAGGGTGGAGATCGCCCACGCGCTCT  661GCCTCTCCGAGCGCCAGATCAAGATCTGGTTCCAGAACCGGCGCATGAAGTGGAAAAAAG  721ACCACAAGTTGCCCAACACCAAGATCCGCTCGGGTGGTGCGGCAGGCTCAGCCGGAGGGC  781CCCCTGGCCGGCCCAATGGAGGCCCCCGCGCGCTCTAGTGCCCCCGCACGCGGGAGCCAC  841GAACCTCGGGGTGGGGGTGGGCAGTGAGTGCAGGGGATGGGGTGGGGGGACAGGAGGGGG  901CCCTGGGGCCTGGGCCCCGGAAAAATCTATCTGCCCTCCCCCACACTTTATATACGAATA  961AACGCAGAAGAGGGGGAGGGGAAGCTTTATTTATAGAAATGACAATAGAGGGCCACGGGG 1021AGGCCCCCCCAGAAGCAAGATTCAAATCTCTTGCTTTCTTTCTTAAAAAAAAGAAAAAGA 1081AAAAGCAAGAAGAAGGAAGAAAGAAAAAGACAGAAAGAGAAATAGGAGGAGGCTGCAGCT 1141CCTCGTTTTCAGCTTTGGCGAAGATGGATCCACGTTTCATCTTTAATCACGCCAGGTCCA 1201GGCCCATCTGTCTTGTTTCCTCTGCCGAGGAGAAGACGGGCCTCGGTGGCGACCATTACC 1261TCGACACCCGCTAACAAATGAGGCCCGGCTCGGCCGCCTCCGCCTCTGCTACTGCCGCTG 1321CTGGAAGACAGCCTGGATTTCCTTTCTTTGTCCCCCACTCCCGATACCCAGCGAAAGCAC 1381CCTCTGACTGCCAGATAGTGCAGTGTTTTGGTCACGGTAACACACACACACTCTCCCTCA 1441TCTTTCGTGCCCATTCACTGAGGGCCAGAATGACTGCTCACCCACTTCCACCGTGGGGTT 1501GGGGGTGGGCAACAGAGGAGGGGAGCAAGTAGGGAAGGGGGTGGCCTTGACAACTCAGGA 1561GTGAGCAGGAAAATTGAGTCCAAGGAAAAAGAGAGACTCAGAGACCCGGGAGGGCCTTCC 1621TCTGAAAGGCCAAGCCAAGCCATGCTTGGCAGGGTGAGGGGCCAGTTGAGTTCTGGGAGC 1681TGGGCACTACTCTGCCAGTCCAGAGTTGTACAGCAGAAGCCTCTCTCCTAGACTGAAAAT 1741GAATGTGAAACTAGGAAATAAAATGTGCCCCTCCCAGTCTGGGAGGAGGATGTTGCAGAG 1801CCCTCTCCCATAGTTTATTATGTTGCATCGTTTATTATTATTATTGATAATATTATTATT 1861ACTATTTTTTTGTGTCATGTGAGTCCTCTCTCCTTTTCTCTTTCTGACATTCCAAAACCA 1921GGCCCCTTCCTACCTCTGGGGCTGCTTGAGTCTAGAACCCTTCGTATGTGTGAATATCTG 1981TGTGCTGTACAGAGTGACAATAGAAATAAATGTTTGGTTTCTTGTGACCAGCAAAAAAAA 2041 AA(Human HOXB4 amino acid sequence-Genbank Accession No: GI:29351568)SEQ ID NO: 3    1mamssflinsnyvdpkfppceeysqsdylpsdhspgyyaggqrressfqpeagfgrraac   61tvqryaacrdpgpppppppppppppppglsprapapppagallpepgqrceavssspppp  121pcaqnplhpspshsackepvvypwmrkvhystvnpnyaggepkrsrtaytrqqvleleke  181fhynryltrrrrveiahalclserqikiwfqnrrmkwkkdhklpntkirsggaagsaggp  241pgrpnggpral (Human HOXB4 DNA sequence-Genbank Accession No: GI:29351567)SEQ ID NO: 4    1GGAAAACGAGTCAGGGGTCGGAATAAATTTTAGTATATTTTGTGGGCAATTCCCAGAAAT   61TAATGGCTATGAGTTCTTTTTTGATCAACTCAAACTATGTCGACCCCAAGTTCCCTCCAT  121GCGAGGAATATTCACAGAGCGATTACCTACCCAGCGACCACTCGCCCGGGTACTACGCCG  181GCGGCCAGAGGCGAGAGAGCAGCTTCCAGCCGGAGGCGGGCTTCGGGCGGCGCGCGGCGT  241GCACCGTGCAGCGCTACGCGGCCTGCCGGGACCCTGGGCCCCCGCCGCCTCCGCCACCAC  301CCCCGCCGCCCCCGCCACCGCCCGGTCTGTCCCCTCGGGCTCCTGCGCCGCCACCCGCCG  361GGGCCCTCCTCCCGGAGCCCGGCCAGCGCTGCGAGGCGGTCAGCAGCAGCCCCCCGCCGC  421CTCCCTGCGCCCAGAACCCCCTGCACCCCAGCCCGTCCCACTCCGCGTGCAAAGAGCCCG  481TCGTCTACCCCTGGATGCGCAAAGTTCACGTGAGCACGGTAAACCCCAATTACGCCGGCG  541GGGAGCCCAAGCGCTCTCGGACCGCCTACACGCGCCAGCAGGTCTTGGAGCTGGAGAAGG  601AATTTCACTACAACCGCTACCTGACACGGCGCCGGAGGGTGGAGATCGCCCACGCGCTCT  661GCCTCTCCGAGCGCCAGATCAAGATCTGGTTCCAGAACCGGCGCATGAAGTGGAAAAAAG  721ACCACAAGTTGCCCAACACCAAGATCCGCTCGGGTGGTGCGGCAGGCTCAGCCGGAGGGC  781CCCCTGGCCGGCCCAATGGAGGCCCCCGCGCGCTCTAGTGCCCCCGCACGCGGGAGCCAC  841GAACCTCGGGGTGGGGGTGGGCAGTGAGTGCAGGGGATGGGGTGGGGGGACAGGAGGGGG  901CCCTGGGGCCTGGGCCCCGGAAAAATCTATCTGCCCTCCCCCACACTTTATATACGAATA  961AACGCAGAAGAGGGGGAGGGGAAGCTTTATTTATAGAAATGACAATAGAGGGCCACGGGG 1021AGGCCCCCCCAGAAGCAAGATTCAAATCTCTTGCTTTCTTTCTTAAAAAAAAGAAAAAGA 1081AAAAGCAAGAAGAAGGAAGAAAGAAAAAGACAGAAAGAGAAATAGGAGGAGGCTGCAGCT 1141CCTCGTTTTCAGCTTTGGCGAAGATGGATCCACGTTTCATCTTTAATCACGCCAGGTCCA 1201GGCCCATCTGTCTTGTTTCCTCTGCCGAGGAGAAGACGGGCCTCGGTGGCGACCATTACC 1261TCGACACCCGCTAACAAATGAGGCCCGGCTCGGCCGCCTCCGCCTCTGCTACTGCCGCTG 1321CTGGAAGACAGCCTGGATTTCCTTTCTTTGTCCCCCACTCCCGATACCCAGCGAAAGCAC 1381CCTCTGACTGCCAGATAGTGCAGTGTTTTGGTCACGGTAACACACACACACTCTCCCTCA 1441TCTTTCGTGCCCATTCACTGAGGGCCAGAATGACTGCTCACCCACTTCCACCGTGGGGTT 1501GGGGGTGGGCAACAGAGGAGGGGAGCAAGTAGGGAAGGGGGTGGCCTTGACAACTCAGGA 1561GTGAGCAGGGAAATTGAGTCCAAGGAAAAAGAGAGACTCAGAGACCCGGGAGGGCCTTCC 1621TCTGAAAGGCCAAGCCAAGCCATGCTTGGCAGGGTGAGGGGCCAGTTGAGTTCTGGGAGC 1681TGGGCACTACTCTGCCAGTCCAGAGTTGTACAGCAGAAGCCTCTCTCCTAGACTGAAAAT 1741GAATGTGAAACTAGGAAATAAAATGTGCCCCTCCCAGTCTGGGAGGAGGATGTTGCAGAG 1801CCCTCTCCCATAGTTTATTATGTTGCATCGTTTATTATTATTATTGATAATATTATTATT 1861ACTATTTTTTTGTGTCATGTGAGTCCTCTCTCCTTTTCTCTTTCTGACATTCCAAAACCA 1921GGCCCCTTCCTACCTCTGGGGCTGCTTGAGTCTAGAACCCTTCGTATGTGTGAATATCTG 1981TGTGCTGTACAGAGTGACAATAGAAATAAATGTTTGGTTTCTTGTGAAAAAAAAAAAAAA( HIV TAT protein residues 47-57 conferring membrane translocationactivity) SEQ ID NO: 5 YGRKKRRQRRR (TAT PTD) SEQ ID NO: 6 RKKRRQRRR(TAT PTD) SEQ ID NO: 7 YARKARRQARR (TAT PTD) SEQ ID NO: 8 YARAAARQARA(TAT PTD) SEQ ID NO: 9 YARAARRAARR (TAT PTD) SEQ ID NO: 10 RARAARRAARA(Antp PTD) SEQ ID NO: 11 RQIKIWFQNRRMKWKK (HSV VP22 PTD) SEQ ID NO: 12DAATATRGRSAASRPTERPRAPARSASRPRRPVE (HeptaARG PTD) SEQ ID NO: 13 RRRRRRR(TAT PTD) SEQ ID NO: 14 YARAAARQARA (TAT PTD-multimer of three)SEQ ID NO: 15 YARAAARQARAYARAAARQARAYARAAARQARA(sense primer for pTAT-HA-HoxB4) SEQ ID NO: 16TAC CTA CCC ATG GAC CAC TCG CCC (antisense primer for pTAT-HA-HoxB4)SEQ ID NO: 17 TCG TGG CTC CCG AAT TCG GGG GCA(sense primer for modified pTAT-HA-HoxB4) SEQ ID NO: 18CGA TGG GGA TCC GGC TAC GCA CGC GCA GCT GCG CGC CAGGCT CGC GCC GGT GGA TCC ACC ATG(antisense primer for modified pTAT-HA-HoxB4) SEQ ID NO: 19CAT GGT GGA TCC ACC GGC GCG AGC CTG GCG CGC AGC TGCGCG TGC GTA GCC GGA TCC CCA TCG

1-232. (canceled)
 233. A method, comprising: (a) culturing humanembryonic stem cells in serum free media in the presence of vascularendothelial growth factor (VEGF) and bone morphogenic protein 4 (BMP-4)in an amount sufficient to induce the differentiation of said embryonicstem cells into embryoid bodies; and (b) adding at least two firstgrowth factors selected from the group consisting of: basic fibroblastgrowth factor (bFGF), vascular endothelial growth factor (VEGF), bonemorphogenic protein 4 (BMP-4), stem cell factor (SCF), thrombopoietin(TPO), Flt-3L (FL), HOX protein, and erythropoietin (EPO) to the cultureof embryoid bodies (c) disaggregating the embyroid bodies into singlecells; and (d) adding erythropoietin (EPO) to said single cell culturein an amount sufficient to expand CD34⁻CD31⁻ human hemangio-colonyforming cells in the culture; wherein the embryonic stem cells, embryoidbodies, and CD34⁻ CD31⁻ hemangio-colony forming cells are continuouslygrown in serum-free media to generate CD34⁻ CD31⁻ human hemangio-colonyforming cells.
 234. The method of claim 233, wherein the VEGF and BMP-4are added to the culture of human embryonic stem cells in step (a)within 0-48 hours of cell culture, and optionally, multiple timesthroughout step (a).
 235. The method of claim 233, wherein the at leasttwo first growth factors comprise basic fibroblast growth factor (bFGF),vascular endothelial growth factor (VEGF), and bone morphogenic protein4 (BMP-4).
 236. The method of claim 233, wherein the at least two firstgrowth factors are added to the culture of embryoid bodies in step (b)within 48-72 hours of cell culture, and optionally, added multipletimes.
 237. The method of claim 233, wherein the at least one additionalgrowth factor is added to said single cell culture, said at least oneadditional growth factor being selected from the group consisting of:insulin, transferrin, granulocyte macrophage colony-stimulating factor(GM-CSF), interleukin-3 (IL-3), interleukin-6 (IL-6), granulocytecolony-stimulating factor (G-CSF), stem cell factor (SCF), vascularendothelial growth factor (VEGF), bone morphogenic protein 4 (BMP-4),HOX protein, thrombopoietin (TPO), and Flt-3L (FL), or a combination oftwo or more thereof.
 238. The method of claim 233, wherein theerythropoietin (EPO) is added to the single cell culture in step (d)after 72 hours of cell culture and optionally, added multiple timesthroughout step (d).
 239. The method of claim 237, wherein the HOXprotein is HOXB4, a functional equivalent or an active fragment thereof,and the functional equivalent or an active fragment thereof possess thesame or substantially similar properties as wild-type HOXB4.
 240. Themethod of claim 239, wherein the functional equivalent or an activefragment thereof, comprises a fusion protein with a protein transductiondomain (PTD).
 241. The method of claim 240, wherein the fusion proteincomprises one or more copies of SEQ ID NO:14.
 242. The method of claim233, further comprising purifying the CD34⁻ CD31⁻ human hemangio-colonyforming cells.
 243. The method of claim 242, further comprising the useof an anti-CD71 antibody to purify the CD34⁻ CD31⁻ human hemangio-colonyforming cells.
 244. The method of claim 233, further comprisingisolating the CD34⁻ CD31⁻ human hemangio-colony forming cells.
 245. Themethod of claim 233, wherein the embryonic stem cells are from a libraryof embryonic stem cells that are hemizygous or homozygous for at leastone majorhistocompatibility (MHC) allele present in a human population,and each member of the library is hemizygous or homozygous for a uniqueset of MHC alleles compared to other members of the library of embryonicstem cells, thereby generating a library of CD34⁻ CD31⁻ humanhemangio-colony forming cells that are hemizygous or homozygous for atleast one majorhistocompatibility (MHC) allele present in a humanpopulation, and each member of the library of CD34⁻ CD31⁻ humanhemangio-colony forming cells is hemizygous or homozygous for a uniqueset of MHC alleles compared to other members of the library of humanhemangio-colony forming cells.
 246. The method of claim 245, wherein theembryonic stem cells are hemizygous or homozygous for allmajorhistocompatibility (MHC) alleles present in a human population,thereby generating a library of CD34⁻ CD31⁻ human hemangio-colonyforming cells that are hemizygous or homozygous for allmajorhistocompatibility (MHC) alleles present in a human population.247. The method of claim 233, further comprising differentiating CD34⁻CD31⁻ human hemangio-colony forming cells into human hematopoieticcells.
 248. The method of claim 233, further comprising differentiatingCD34⁻ CD31⁻ human hemangio-colony forming cells into human endothelialcells.
 249. A method of administering to a patient in need thereof, thehuman hematopoietic cells of claim 2477, comprising: selecting thepatient; providing a quantity of hematopoietic cells; and administeringthe quantity of hematopoietic cells to the patient.
 250. The method ofclaim 249, wherein the patient is in need of a blood transfusion.
 251. Amethod of administering to a patient in need thereof, the humanendothelial cells of claim 248, comprising: selecting the patient;providing a quantity of endothelial cells; and administering thequantity of endothelial cells to the patient.
 252. A method of expandingCD34⁻ CD31⁻ human hemangio-colony forming cells, comprising: providing aquantity of CD34⁻ CD31⁻ human hemangio-colony forming cells; and addingat least one growth factor in an amount sufficient to expand CD34⁻ CD31⁻human hemangio-colony forming cells, wherein the CD34⁻ CD31⁻hemangio-colony forming cells are continuously grown in serum-freemedia.
 253. The method of claim 252, wherein the at least one growthfactor is selected from the group consisting of: insulin, transferrin,granulocyte macrophage colony-stimulating factor (GM-CSF), interleukin-3(IL-3), interleukin-6 (IL-6), granulocyte colony-stimulating factor(G-CSF), erythropoietin (EPO), stem cell factor (SCF), vascularendothelial growth factor (VEGF), bone morphogenic protein 4 (BMP-4),HOX protein, thrombopoietin (TPO), Flt-3L (FL), and combinationsthereof.
 254. The method of claim 252, further comprisingdifferentiating CD34⁻ CD31⁻ human hemangio-colony forming cells intohuman hematopoietic cells.
 255. The method of claim 252, furthercomprising differentiating CD34⁻ CD31⁻ human hemangio-colony formingcells into human endothelial cells.
 256. A method of administering to apatient in need thereof, the human hematopoietic cells of claim 254,comprising: selecting the patient; providing a quantity of hematopoieticcells; and administering the quantity of hematopoietic cells to thepatient.
 257. The method of claim 256, wherein the patient is in need ofa blood transfusion.
 258. A method of administering to a patient in needthereof, the human endothelial cells of claim 255, comprising: selectingthe patient; providing a quantity of endothelial cells; andadministering the quantity of endothelial cells to the patient.
 259. Amethod of inducing tolerance in a human subject receiving a donorallograft, comprising: (a) creating thymic space in the human subject;(b) depleting or inactivating donor-reactive T cells in the humansubject; (c) introducing into the human subject, the humanhemangio-colony forming cells generated by the method of claim 1,wherein said hemangio-colony forming cells are match with respect to thedonor, and (d) implanting the allograft into the human subject, whereinsaid human hemangio-colony forming cells induce tolerance in the humansubject to the allograft.